Does the error message mean that "An Internal Error Has Occurred" ? If yes , you need to submit a ticket includes your user account and your ftp account so that our developer can debug it on your site
Thanks to all for the comments. Actually I do not face this error. Only a user of my site got this error and sent me a screenshot. I'm not sure whether the problem is in my site or user's browser...
Could you be able to replicate the error, Moo Fan? Let us know if we could help debug if the issue can be regenerate.