I had a problem intially with webmail and I found the error was because of mysql.pm was old. I upgraded it through WHM and fixed. Now there is no problem.
I had problem with horde webmail & eximstats .I changed Mysql password and now eximstats work well. but I cant open the horde directely from my cpanel.
are you guys using the stable or edge etc... release? which one I only ever use stable on my production machines. and I haven't had any of the problems as stated above.