What can interfere with a drug test and cause you to test positive for ecstasy or MDMA?

I have a friend who tested positive for ecstasy when given a drug test. She hasn't done any ecstacy, but she has done other drugs. What can cause you to test positive for ecstacy?

: http://alcoholdrugstreatment.info/what-can-interfere-with-a-drug-test-and-cause-you-to-test-positive-for-ecstasy-or-mdma