Hi

This was addressed in Crystal Reports 2008, while creating parameter it self it will ask you to check a box if the parameter has multi selection.

Work around for this problem is:

Create a blank report, with a parameter (if this is dynamic then select the table else select static values)
Now, insert your report as sub report and link main report parameter to sub report parameter. Then go in command where clause mention some thing like :

{databasefiled} in ({?parameter})

Thanks,
Sastry