Форуми / Cotonti / Support / Polls error

Some of my users (not all) are getting this error when they try to vote

"The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the administrator and inform them of the time the error occurred, and anything you might have done that may have caused the error."

Rights: set for all
plugin config:
Number of polls displayed : 1
Poll display mode : recent polls

Polls config:
Vote counting method : ip
Max number of options : 100
Force duplicate option removal : yes

P.S I thought this was an index polls problem only, but it seems to be a polls problem overall so if an Admin can move this to SUPPORT, that would be great.