What are the disk types (ide, or scsi)?
What are the virtual disks names?
In some cases snapshots don't show up in the Snapshot Manager although there are active snapshots. In case virtual disks names look like "<vmname>-00000x.vmdk", then it's most likely a snapshot. Assuming you do have sufficient free disk space, you may then create a new temporary snapshot, and then run "Delete All" from the Snapshot Manager.
André