Probably, try posting your formulas, and where the subreport is.
I common problem with variables is that it will be based on a NULL, so the result is NULL. You can turn on the File->Report Options->Convert Null Values to Default to avoid null problems.
Of course this is a wild guess as you've supplied nothing technical.
Saying soemthing doesn't work won't help describe a problem, you need to do some work if you want help:
Crystal version
Database/connectivity used
Example data (tables/fields/data/formulas)
Expected output
-k