OK tried this, so my select snippet is:
Select EventName, 'server.htmldecode(' + EventDesc + ')', RepeatType... etc
and I get this error:
Invalid operator for data type. Operator equals add, type equals ntext.
so it would appear that I can't do concatenation with EventDesc as it's a text field.
I can however, if I use substring eg:
Select EventName, 'server.htmldecode(' + substring(eventdesc,1,1024) + ')', RepeatType... etc
but then I just get server.htmldecode(<p>... written out to the browser.