First it was the whole mess with his twins that triggered a lawsuit, and now another legal problem.

Seems Dennis believes he got stiffed on a $70,000 loan. So he's suing New Yawker Steven Mendelson claiming the 2001 loan has gone unpaid and Quaid wants his jack back.

In the lawsuit filed in L.A. County Superior Court, Quaid claims Mendelson defaulted on the loan more than 4 years ago, but it seems they went back and forth trying to resolve their dispute but ultimately couldn't.