Unable to upload user avator only for one specific user

[Yuxue Entertainment]

I created many accounts in my jira software. 

The upload user avator functions well for all accounts at first. But after one account tried to upload a big BMP file as his avator and failed, he can't do it good anymore. Anytime he trys to upload a user avator in any size and any format, the page prompts "Cannot attach file xxxx.jpg: Unknown server error". No detailed errors can be found in log file expect a 403 error. At same time, the other accounts can do it well still.

What happend? How to fix this problem?

[Alexander Pappert]

maybe there is some error in the logfiles

can he change back to a jira avatar?

if you are server admin, you can go in his public profile and try to upload a new avatar for him, maybe it works with your account