Usergroups and styles

[Delw]

I wasnt sure were to post this so If this is the wrong place I am sorry.

I am running v3.6.3 with a few mods installed, when I goto change a to a different primary user group the styles get all messed up most of the nav bar is missing and all the text on the forums turn white.

if I make it so they get a secondary usergroup I have no problems, it only happens under a primary user group.
this includes the banned user group coppa user group and a few others

Where do I start looking?

Thanks
Delw