Chris,
Somewhere in your query behind the report, or... on the report itself,
you have a reference to a field or value that does not exist. The Enter
Parameter Value dialog box should indicate what it's looking for.
Run the query by itself, and if you get a propmt, then that undefined
reference is in the query. If the query runs clean, then the parameter must
be on the rpeort. It could be in a calculated field, or even a subreport,
or even in the Grouping and Sorting list.
You just have to dig it out... no one can tell you where it is.
Another method is to make a backup copy of your report for safekeeping,
then go into your original report, and Cut out many of the controls you
placed on there. Run the report.
Still have the prompt? Then the Parameter must be in the few fields left
on the report.
Doesn't prompt? The the Parameter must be in the fields/subreports you
just Cut... Paste them back on your report, and take out a smaller group
this time, and repeat the process. Keep doing that until you find the
culprit.