First of all, sorry for posting the same conclusion that Vaclav posted :-( I think what threw me off was Vaclav saying the error occurred in C51 V5.50 and not in V7.01. I had tested it using V7.01 and did get the error, so my skimming what Vaclav said lead me to believe that his V5.50 comments didn't necessarily apply.

Nevertheless, my V7.01 does produce the error, at least when invoked from the command line, but removing one SRC or the other like Vaclav says corrects the error.