Hi @Arash Nosrati Heravi,
Based on your description of the problem, I'd like to ask a couple questions:
- Are you encountering this error in the Outlook client or in OWA? (If it's in the Outlook client, which specific version is being used?)
- When did your problem start to occur? Did you do anything prior to the error that might have caused it?
- Is the account you are logged into an Exchange account? If so, what is the version of Exchange Server?
- Is the error occurring for all users, or for individual users?
You could try the following suggestions:
- If you are using Outlook, update the Outlook version to the latest.
- Recreate the Outlook profile. Refer to the following documentation on how to create an Outlook profile: https://support.microsoft.com/en-us/office/edit-an-outlook-profile-e93ea161-f742-4119-bfa1-9dca4c3e48fa
- If the problem persists, I suggest that you attach a screenshot of the error so that I can better understand what the problem is.