serious problem using SOS 3.5.3

I am encountering a reproducible problem using SOS 3.5.3.  If I try to do a
"Get Latest Version" on my solution after another developer has added any
projects to the solution, I get the sequence of errors illustrated in the
attached jpeg image.  I also get this sequence of errors if I delete my
solution folder and try to get the project from source control.

 

I would appreciate any input on how to proceed.

 

Thanks!!