When copying text from an HTML formated Outlook message into a comment to a JIRA ticket, we get the error shown in the screen shot.

We debugged this the following way:
1. Copy text into Windows Editor; this shows some control characters.
2. Delete control and - just to be shure - other special characters.
3. Copy this clean text into the comment in JIRA - all is fine.

We did not check wether the same happens if you copy the control characters into other issue fields like description or summary.