So, after getting around the out of memory error by only using wave files, I then had X2 producer crashing regularly. Sometimes it was when adding a softsynth (usually Z3TA 2.1) and others when addings effects. I've been reading various forums about the best way to run X2 producer, so I figured I'd just do them all and see what happens. So, I finally bit the bullet and reloaded the whole lot. I have 2 hard drives in my PC, and cleared one off and loaded X2 producer on there, as well as the quickfix. Then loaded all the additional instruments etc, and loaded the projects onto a seperate external hard drive. So far everything is working, except I bought an Andy Jonhs kit for session drummer 3 and that isn't loading all the drums correctly, so I'll need to reinstall that. Anyway, so far so good, no memory errors (even when I load audio files that are not wave files), and no crashes. In fact it seems more stable than it's ever been.
I've also been turning off the internet connection and the security software when I use X2, so I've done everything I can to minimise any problems. I guess the thing is I don't know which actions fixed the out of memory problem or the crashes, but as long as I have something that works I'm happy. I've not loaded the X2 'a' update yet, as the out of memory problems started after I loaded that. I'll back up all the cakewalk stuff from my second hard drive then try installing the update again. If the out of memory problem comes back, then it has to be something to do with the update, and that being the case I'll just copy the backup files and run X2 without the updates.