Got this from my client today that was getting errors when adding an issue:
Okay - I think I figured it out. The error occurs when the text of issue summary exceeds the number of allowable characters. To reproduce the error I pasted the text in the comment below into the summary field. Then I went to the end of the text and pasted it again and hit the create button. There is no indication that there is a character limit and apparently I was permitted to enter more than the field will hold.