compile fails with "Specified minimum required version is greater than the current publish version. "

I have been compiling my build without problems for the last year and all of a sudden I get this error when I try to do a compile:

"Specified minimum required version is greater than the current publish version. Please specify a version less than or equal to the current publish version."

What does seem to be connected is that I am working on a maintenance branch that is different than my main line: that is when this happened.

Any ideas?