Garageband: synchronising audio and midi error while recording

Every time I try and record through garageband with my Rode NT-USB mic it either won't record and pops up with

+"GarageBand: Error while trying to synchronize Audio and MIDI.+

+Sample Rate (different amount every time) recognized.+

+Check conflict between GarageBand and external device."+

Or it records, but when played back the recording skips like a scratched cd.

If i record with the built in mic on the macbook it records fine, and it used to work fine with the Rode mic.

So I'm a little lost...

Other info: Mic is set up as the audio input and output device in both system settings and garageband preferences.

Any help would be appreciated.

Thanks.