Whenever I click on "My Posts" I get the following error

"ORDER BY items must appear in the select list if SELECT DISTINCT is specified. 0"

I know this is an SQL error and I'd know exactly what to do if this was my SP, but is this a sign of some other problem or already known about.

Thanks very much, that does look like the answer.  I'll try it this evening.

The link gets there for me - I'm copying the final answer - at least in my case below.

For those like me who are new to DNN/SQL Server and such, the stored procedure that this fix has you modify resides inside the DotNetNuke Database.MDF database (assuming your database is named the typical/default: Database.mdf).  And if like me you do not know much about coding stored procedures let alone modifying them, you might use SQL Server Management Studio Express to Attach to the Database.mdf, then make your way down into Programmability > Stored Procedures > Forum_SearchGetResults - and make the change below to that stored procedure.

Before: @Filter + ' GROUP BY P.ThreadID , P.CreatedDate ORDER BY P.CreatedDate DESC '
+After: @Filter + ' GROUP BY P.ThreadID , P.CreatedDate ORDER BY P.ThreadID '

After you've modified the stored procedure, right-click and Execute to run/save the change.