I am having the same problem. I wonder if I am entering my sources correctly in FTMM2 for the Mac or if it is a glitch in the program. My method is from within FTMM2 I enter a fact, then let's say I enter a new source (Marriage Records from Whatcom county), and enter a citation detail to accompany that fact. All goes well.
But, then, let's say I now have another individual who has a Marriage Record from the same source, but a different page, so I use the same source, but enter new citation detail and upon uploading to Ancestry.com I get the error, "Untitled Source." Yet, I think I've used the correct procedure for entering sources and citations within FTMM2 but it doesn't yield a desirable outcome on Ancestry.com.
Am I doing something wrong?