Somehow in between your two posts this:
It looks like your database search code is on the page twice... did you run it multiple times on the same page without clearing the page? That might be the root of some of these problems... you may want to delete or clear the page and try again.
To simply fix the error replace:
$WADbSearch1 = new $WADbSearch1;
$WADbSearch1 = new FilterDef;
but it appears there may be more issues since it really shouldn't appear twice like it is in your second code example.
The code looks correct in the first one other than the missing include file, so I'm not sure what else might have changed which is why I would probably start over.