To me it's like this
If NOT InGroup("Some group") OR @WKSTA="PCNAME"
? "Condition met"
Else
? "Condition not met"
EndIf

the or statement is of a higher order so what happens is this
If NOT ( InGroup("Some group") OR @WKSTA="PCNAME" )
What you want is possibly
If ( NOT InGroup("Some group") ) OR ( @WKSTA="PCNAME" )