can't reduce the primary data file after moving data out to secondary data files using partitioning

Hi,

I have used table partitioning to split the data from primary data file into multiple data files for easy manageability but i am not able to shrink the primary data file after moving the data out to the secondary data files.

I have tried shrinking just the data file using truncateonly option but it doesn't actually do anything.

Any help would be much appreciated.

Thanks

Arshad