Gig from hell...
I had a video editing gig that included playing a preview of the final product to a room full of MoneyBags as a small part of a fundraising dinner.
I tested my set up the night before:
MacBookPro 15" 2.33Ghz Core2Duo, 3GigRAM OS 10.5.8 .
Express34 card to RPM Driver 2.67, rev13
RPM to house audio via balanced TRS
Laptop hooked by DVI to projector

I created a new user account for this. All notifications (Growl etc) turned off, all wireless/bluetooth disabled. Desktops set to neutral colours.

It had worked the night before in my tests but on the day the RPM would consistently come up as a DigiFace and no audio would come out. I rebooted at least 3 times trying different card insertion orders and it come up the same each time. The time to set up I got from the AV people was not a lot and I was pretty panicky. Sweating buckets. Luckily I had brought a ton of other cables and went with the headphone out from the laptop and into RCAs on their board. I had been asked to provide balanced 1/4" source by AV the week before which is why I went with the RPM in the first place.

I remember having this problem when I first got the Express34 card but not since. I know I need to upgrade the drivers on the laptop.

Most frustrating? Firing up the laptop this morning and having everything come up RPM and roses. WTF!
Lesson learned... I dunno, keep your drivers updated and carry spare cables?