Please help - Sample rate could not be set.

Hi I’ve been recording a new EP via cubase 5 and had been loading in some new plugins… then opened a project and now I keep getting the following message…

Samplerate could not be set. This may be due to the sampleclock being set to external sync.

Im using Edirol UA25 and I really really cannot afford to lost these songs. I’ve looked at previous posts and couldn’t get in to work, does anyone have any idea how I can get this to work? I get this message whatever I try and open.

Many thanks