It sounds as if you might be running into the maximum number of images AE can import as a single footage item. However, let's eliminate the obvious. Can you confirm you're importing a sequence as a single footage item?
Unfortunately, the link above doesn't list the maximum number of images AE allows in a sequence; it would be helpful if it did.
Yes, it's being imported as a single footage item. We've imported up to 30,000+ frames on occassion (if the planets are aligned properly, and it's the 5th Sunday of the month), but generally it'll lock up or hang for up to an hour.
It's not uncommon to have to import large numbers of frames as a sequence. I'm puzzled why this would give AE a hard time. The box I typically use has dual xeon procs and 24 gigs of RAM. My machine is certainly not the issue. Anyone know of a technical hurdle I'm running into?
What file formats and how are they numbered? Some file formats use an awful lot of memory and are generally slower than others. Conversely, numbering files without leading zeros has been known to slow down things considerably, as AE will need to scan the entire sequence first, than sort it properly...