Hi Lauren,
The second issue that you asked has really no relation to the issue at hand. You see less values in the parameter drop-down because CR limits the list to 1000 values for performance reasons.
You can increase the values in the list by editing/creating a registry key.
Go to regedit (start > run > regedit) Browse to the location:
HKEY_CURRENT_USER\Software\Business Objects\Suite 11.5\Crystal Reports\DatabaseOptions
Create a new key called 'LOV' here and then on the right-hand side create a new string value called 'MaxRowsetRecords' with a value higher than 1000, perhaps around 10000.
It's still strange that you see that error when you try to edit a parameter. Did you try creating a new one on the existing report or a new one?
-Abhilash