How to Fix “ Outlook Not Supported Calendar Message.ics ” : Compatibility Issue in Outlook & IBM Notes

Raj Kumar ~ Modified: 2019-10-15T09:58:21+00:00 ~ Outlook Error ~

The ICS file format is used by the many email applications to store calendars. It is a universal file format that allows users to print and share calendar’s details on the cloud and over email. It is used by Microsoft Outlook 365, 2016, 2013, 2010, Google Calendar, and Apple Calendar, etc., email clients. The main role of ICS is to send the meeting requests to users within or outside the organization, so that they can easily import that event in their calendars.

But every email client has a different recurring pattern, which sometimes starts creating issues like not supported calendar message.ics. Now, to access calendar and its event in a proper way one needs to resolve not supported calendar message.ics issue as soon as possible.

User’s Real-time Scenario

“When I received a meeting invitation as a normal message with some attachments in Outlook 2010. Among all, one attachment is not supported calendar message.ics. I did not understand what does it means because when I tried to open it displays an error message The operation failed. Why I am not able to open this meeting invitation and how it can be fixed so that it can easily be opened in my calendar?”

It should Look like this (without error)

In most of the cases, the meeting invitations are sent by IBM Notes users that include some recurring patterns, which are supported by Outlook’s recurrence pattern. At that point in time, it becomes really difficult for the users to access the calendars normally. This blog will let users know how to fix ” Outlook not supported calendar message.ics ” in an efficient manner.

Different Recurrence Patterns of Lotus Notes

The Recurrence Pattern followed by the calendar in Lotus Notes is very different from the one used by Microsoft Outlook. Here are some example of incompatible recurrence patterns and options:

1. Exceptions for weekends

  • Delete
  • Move to Friday
  • Move to Nearest Weekday
  • Move to Monday

2. Recur monthly: Xth day counting from the backwardness of the month
In this case, it is not broken, but unable to count backward so display wrong dates in MS Outlook.

Different Methods to Open ICS File by IBM Notes

If Outlook 2016, 2013, 2010 is unable to open ICS file end by IBM Notes, then a user can try to open it with the help of another application also. All possible ones are discussed below:

Open ICS File With Windows Calendar

Microsoft Windows 10 Calendar App is capable to process the ics-files created by IBM Notes. Thus, if a user is using or Microsoft Exchange, then he or she can easily configure that account the Mail App on Windows 10. This way the ICS file calendar is easily available in the Calendar app. Whenever a user try to open that unsupported calendar message.ics file via Calendar app, this meeting is uploaded and sync with Microsoft Outlook also. Now, to do the same, follow the steps mentioned below:

1. First of all, you need to save the “not supported calendar message.ics ” file on the desktop of your machine
2. After that, right-click on the same file and select Open With >> Calendar option
3. Here, it will ask you “Which calendar would you like to add these events to?”. Simply, choose Exchange or Calendar
4. Then, click on the Add to calendar button
5. Now, wait for a few minutes, this Meeting is added successfully to your Calendar in Outlook.

Drawbacks: This meeting is added in Appointments and first occurrence of meeting might be added twice in the Calendar.

Open ICS File Via Google Calendar

A user can also use Google Calendar also to open and access ICS files and avoid Outlook not supported calendar message.ics. Here, a user needs to forward the message to his/her Gmail ID and open the same Gmail account in the browser. Here, in the “Event in this message” box, it shows “Add to Google Calendar” link. Click on the link are you almost done. Now, to access it in Outlook, follow the steps below:

  • First of all, you need to connect your Google Calendar with Outlook
  • After that, add your alternative email address as a Guest
  • Then, go to Calendars >> Meeting and add the address in the Guests section.
  • At last, click on the Save button.

This way also a user can open an ICS file in Microsoft Outlook. But the process is quite long, time taking and complex to perform.

Prevent Sending Incompatible Calendars from IBM Notes

Both Administrators & Lotus Notes users can edit the Notes.ini file to prevent sending out the incompatible ICS Files from Lotus Notes Client

Changes to be done in Notes.ini

  • Set Value of $CSCompatibilityMode = 2
  • DisallowRelatedIcalendarMIME=1

Note : 

$CSCompatibilityMode = 2, denotes  how the selection box ” Some invitees use other mail programs” (as shown in below fig) will behave:

0 = Option is hidden & turned off
1 = Option is hidden & By-default is turned on 
2 = Option is displayed & By-default is turned off
3 = Option is displayed & By-default is turned on & locked

Once these changes are completed in Notes.ini file, IBM Notes will provide you with following option, ” Some invitees use other mail programs” which will prevent you to set recurrence, that are not supported in other email clients

An Alternative Approach to Fix “ Outlook not supported calendar message.ics ” Issue

If any of the above-discussed approaches are not able to resolve the compatibility issues between Outlook 365, 2016, 2013, 2010 and IBM Notes recurrence pattern, then it suggested switching to some third-party solution. SysTools ICS Converter is one of the application that permit users to export into PDF, PST, CSV, vCard and many other file formats. A user can try this application to convert received the ICS file from Lotus Notes to any of the desired formats. After that, one can easily open it any of the supported applications without any compatibility issue. The software keeps the file structure intact and does not impose any file size limitation.


Scheduling meetings and sending invitations is the common task that needs to be performed by almost every business user. But it becomes very uneasy for the users to open incompatible recurrence pattern ICS file. Users generally encounter Outlook not supported calendar message.ics issue. Thus, here we have covered all possible ways to open the ICS file. Moreover, if a user wants to convert the ICS file, then they use the third-party tool discussed above.

Frequently Asked Queries by Users

1. I am unable to open meeting invites sent from Lotus Notes. How can I resolve this issue?

Above in the article, you will get the proficient and effective solution to fix your issue. Using the above suggested application, you can easily get rid of the problem.

2. Can I fix Outlook 365 not supported calendar message.ics issue?

Yes, with the help of above recommended automatic method, you can easily repair Outlook 365 not supported calendar message.ic problem without any hassle.

3. How can I repair not supported calendar message.ics in MS Outlook 2010?

The free manual solution having some limitations. In this situation, a third party application can work appropriately. So, using the ICS converter tool, you can resolve this issue without any compatibility issue.

4. Does the tool take too much to repair the issue?

No, the software takes a few minutes for resolving this ‘Outlook Not Supported Calendar Message.ics’ error.

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