Pro Tools problem

[HA_DA_JA]

Pro Tools ver LE 8.03 on a mac with digi 003R
I open a previous session record a vocal track to a backing track with low latency monitor on it for monitoring while performing and upon playback the audio is not syncing up with the previous backing track. During recording it all sounds perfectly fine.
I must have dome something simple because this is unusual and has not happened before.
Come to think of it I did just recently patch in via sdif the Lexicon MPX1 but this is not being used during the session and I cant see why that would be causing problems.
Any suggestions?
Thanks

[mylesgm]

Check your clock. It's possible that the oo3 is clocking off the spdif whilst Protools is set to a different sample rate. Is pitch a problem with the new tracks?

[geofflee]

Have you got any sample-hungry plugins on the master fader? You could be hearing the backing 'late', causing your newly recorded tracks to be out of time.

[The Tasmanian]

First - check "SPOT" to make sure the vocal is where it should be - just to make sure you did not nudge the vocal (which is easy to do)

[HA_DA_JA]

Excellent suggestions.
I found my problem I forgot to bypass the plug ins on the Master outputs when I was retaking a vocal.
How dumb was that.
Thanks
Dale