If you are wanting to shrink the data file, did you select the "Shrink", "Files" and "Reorganize pages before releasing unused space" dialog box?

If you are wanting to shrink the log file you may have to run a TLog backup if the DB is fully logged as a VLF may be in use. To determine if a VLOG is in use run the following command (the TLog will only shrink from the bottom up until it hits an active VLF):

DBCC LOGINFO (DBNameHere)

A "2" in the status field of the LOGINFO command indicates that that VLF is in use. You may need to run a TLog backup again before shrinking the log file (look for all zeros in the status field then shrink the TLog).