Yep. Technically this is trying to use summary in a summary wich is not allowed.
Instead of the group select you can use a suppress statment to hide all the records that do not meet your criteria. This menas all of your display needs to be in the footers.
Create a Running Total (you can also use shared variable fomrula if you prefer)
Name=HideFlag (or whatever)
Field to Summarize=clientid
type= count
evaluate=use a formula
table.statusdate=max(table.statusdate,table.department) and table.status in ["A","W"]
Reset= on a group (group 2 department)
palce in group 2 footer.
You can now use this value to suppress the footers where #HideFlag=0