Are there any issues with using jQuery 1.5.x with jQuery UI 1.8.x??

Because we’re having issues upgrading to jQuery 1.5.1, Is this version not compatible with jQuery UI 1.8.x which we also use heavily?

Here's the error we're getting:

TypeError: cache[id] is undefined

on this line of code: 

cache[ id ].toJSON = jQuery.noop;

Thank you!