Eric, these are very different issues. For starters, this forum is still 4.4.3, while the other poster is using 4.5.3 of the module. The issue you are seeing is a well known issue from 4.4.3 and was resolved in 4.5.3 (Its so old, I don't feel like digging out the solution/problem but it has to do with your notifications, if you clear them out completely you won't see the issue - just don't subscribe to a thread again and use only forum level notifications).
As for the original poster, this has nothing to do with other modules or permissions. There is something the system is expecting at the 'Post to Database' method that it is not receiving. Below is a list of items it is expecting, one of these are nothing and shouldn't be. Looking at the URL of the original post, I think the basics are there. I would check to see if you can find the forum user in the db (Forum_Users, pass in UserID and PortalID to see if you get a match via SQL).
Int32 TabID, Config objConfig, Int32 PortalID, ForumUser objForumUser, String PostSubject, String PostBody, ForumInfo objForum, Int32 ParentPostID, Int32 PostID, Boolean IsPinned, Boolean IsClosed, Boolean ReplyNotify, Int32 ThreadStatus, String Attachment, String RemoteAddress, Int32 PollID, Int32 ThreadIconID, Int32 ParentThreadID, Boolean ProcessParseInfo, PostAction objAction