This issue is a problem in the core, which is triggered by the Forum module. The problem is that the forum module looks for various modulesettings when you display the member list. One of them isn't there - 'Column_PostCount', and isn't set by the Forum module. Here is a link to a post about the problem on Crispy's site - http://support.dotnetnuke.com/issue/ViewIssue.aspx?p=0&id=7003 (the site is down at the moment, since the database seems to have run out of space). Also a Gemini ticket - http://support.dotnetnuke.com/issue/ViewIssue.aspx?p=0&id=7003.

I'm pretty sure DNN 4.8.1 solves it, also Forums 4.4.4 when released will solve it. However, if you can't install either of these, you can insert a record into the module settings table to solve the problem. You need to insert one for the User Account Settings module. From memory this is somewhere around module 357, but varies portal to portal. Also to confuse, there are actually two module sets - one for the portal, and one for the host. Anyway look for other module settings with the name format Column_######, there should be several for a single module. Insert a record the same with Column_PostCount with a value of True.

Cheers
Roger