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Int32 to String casting errors
Your last version has problems with casting Int32 to String and other way around. I tracked this down to some lines in you Comment, Forum and Topic models, in the attachment you will find a patch file to solve the issue.
In short, your database model uses Int-fields for MemberID, AuthorID, etc. But your code tries to put Strings into them, which throws up exceptions.
Thanks for this awesome project.