Help with latency issues (I think)

I've never had problems with Reaper before, but lately it just seems to be performing really poorly. For instance, I could always set up the click in Reaper and record something while listening to the click, and when I played it back, my performance would still be in sync with the click, but when I did some overdubs the other day, the vocals were always way off. I would record the guitars first and then play them back while the vocalist sang, but after the recording was done, I'd play everything back and then vocals would be at least half a second late. I'm using the latest Mac build and going through a Saffire Pro 10 i/o. My computer is a MBP with a 2.14 Core 2 duo and 2 gigs of RAM. The latency is listed in the Reaper title bar as 12/12 ms. Also, Reaper has a lot of trouble playing back files with multiple tracks (let's say 5) that have plug-ins on them. I feel like my computer ought to be good enough to handle that, but maybe not?

It's not VSTs, I'm only using the supplied ones :( I thought it would save me some power by putting one reverb effect on the master track instead of several different ones on other tracks, but that actually made it much slower. Uh... what?

I don't know Macs but I know what I would try. Start new project.Set it up for my sound card and the use Reaper's explorer to drag the tracks from the problem project and build a new project a test.If that works then it must have been a setting somewhere. I have an ageing AMD 3800 and 1 gig of ram but I don't usually do songs with too many tracks.The most I've used think was 12. Again I did get a sync problem exactly like yours but cannot for the life of me remember what I did to cure it which was a different problem than that rogue VST :( It may have had something to do with the Metronome settings?I use a 2 bar count-in with the Metronome enabled but most times have it disabled once the part starts to record?

Here's the really strange thing I don't get. When I play back the original guitar recordings with the click track, they all line up like they're supposed to. It's just the vocal overdub that is way off. It did that in two different recordings. I really don't get it because I know I've done overdubs for bass before with far more active tracks and not had any problems. I don't know why a setting would have just magically changed, but maybe I don't have something right?

On the track that is bad syncing is the,"Monitor" option still on it in it's Record button options? This kind of thing bugs the hell outta me<grin>.BTSTGTTS :O

Nope. I didn't even have it on during recording, I don't think, because I can just monitor the input on the interface instead. If I do it with the monitor button, then the latency kicks in and there's a delay before you can hear the voice coming back out.

I don't know if this has anything to do with it, but both the interface and my external hard drive are running through the built-in firewire ports on the MBP, the hard drive through the 800 and the interface through the 400. I assume that they are on the same bus or whatever... would that have anything to do with it? If I was to get an expresscard adapter, would that help?

Have you checked that all your drives are in DMA mode?

What does that mean? And how do I check that on a Mac? I seem to remember checking that on Windows for Pro Tools a long time ago, but I don't think I ever had to do it on my Mac.

Sorry.My mistake.I don't know how the hard drives work on Macs :(