If you are still smelling something musty there is still probably a moisture issue.
I have seen this to be caused by moisture entering the home due to air leaks but more often than not there is an adjacent slow water leak. If there is a water source near by, I would suggest investigating a plumbing issue and/or having a professional investigate behind the wall that was showing mold.
For more information:
Read "How do I know if I have mold in my house?" a Q&A answered by Sean Lintow.