Britney Spears was set to perform at Cyndi Lauper's True Colors tour at L.A.'s Greek Theater on Saturday but had to cancel because she would only dance or lip sync and Cyndi wasn't having any of that. A source tells Page Six:

"There's no way. Britney said she would only dance or lip-sync - and to be on stage with Cyndi, you have to actually perform. It's not happening now."

So Britney Spears will only sing on stage if she doesn't ...