It's not a plugin that is causing this. It's the wordpress multisite feature! After activating this feature, the problem started to happen. Even checking many comments about the problem, I'm not sure if it should not be interpreted as a major problem.
My users claim about this! Because most os my users try to input uppercase letters, because they sign up at my site using their company's login. The error message it's not helpfull either. So, all the time they send emails saying that they can't understand what's going on whem this error occurrs in this sign up process. It should be transparent for users!
What's confusing me, is that the error happens in the classipress php source code and if it can really be fixed by a plugin. Why wordpress' guys didn't fixed that? So, it's not so clear. I avoid using so many plugins, because every time I need to upgrade wordpress/classipress, I only can do if all the plugins have compatibility.
I created another thread, related to the same problem, in another forum and Bleem it's trying to warn us about this.
Do you understand my concerns?
Originally Posted by samcy