Sorted it guys, and yes the bit rate was at fault. Some backing tracks had been saved at 48000hz rather than 44100, and audacity had switched to that and kept it so for saving. The chaps over at the audacity forum suggested I switch the bit rate manually to 44100 for these tracks and hey presto, we're back in the game! Thanks to everyone who chipped in to help.
As a side note, some things that don't seem to affect me at all were suggested here such as file name length, file extension in capitals, and usb disconnect procedure. I have flouted all the perceived wisdom on these regularly, seemingly without incident, mainly because I do struggle with software issues normally - I'm quite a luddite when it comes to computers. Once again though it has come down to bit rate/sample depth compatibility. All good fun if you're learning I suppose.
As a side note, some things that don't seem to affect me at all were suggested here such as file name length, file extension in capitals, and usb disconnect procedure. I have flouted all the perceived wisdom on these regularly, seemingly without incident, mainly because I do struggle with software issues normally - I'm quite a luddite when it comes to computers. Once again though it has come down to bit rate/sample depth compatibility. All good fun if you're learning I suppose.
