Software Build and Release Specialist

I ran into another not-so-clear Perforce error message today while trying to import a new project to an existing depot.  I had a new project1 which I wanted to import into the existing // depot, but when I tried to add via P4V or ‘p4 add’ in the command line, I kept getting this message:
D:\Work\P4>p4 [...]

Ever run into this error with Perforce’s ‘p4 changes’ or any other similar command?
//projectfoo/bar/… – must refer to client ’some_p4_client’.?
I ran into this exact problem today.  I was trying to do a ‘p4 changes //projectfoo/bar/…@xxxxxx,yyyyyy’ to get a history of the changelist and got that error. The symptoms were that doing the same command on [...]