I have had this no end of times with MX and it didn't really
have any major effect on my files. I still get it with pages
created in MX when I open them in my CS3. I often just used to
restart DW and it would go away.
However, you could go to your code view and locate the
recordset sql, copy it, create a new recordset, then either paste
the sql in the advanced window, or just create a SELECT * FROM blah
blah, click OK and then find the new recordset sql code (in code
view) and paste the old sql code in place of the new. Then delete
the old recordset and probably best while in the code view rather
than the server behaviours panel as this panel might remove any
dynamic content related to the old recordset.
Of course doing this has knockon effects with everything
dynamic on your page, so you will need to do a find/change so that
any content referring to your old recordset is update to the new.
If that don't work, save a copy of your page, strip all
dynamic related content out and start again.
These are painful methods sometimes, but they often resolved
my problem.