I'm not aware of any limitations regarding the # of variables you can use. We had a parsing issue bug in an early version. Would you be able to share a template with us with which we can reproduce the problem? What version / Data System are you using?
I just wanted to follow-up to see if the last reply helped or if there were any other questions. I also update the tags on this post to make it easier to search.
I went ahead and flagged the "Correct Answer" on this post. If you still need help though, please let us know and we would be happy to continue working with you.