I don't think your problem has any thing to do with number of frames or their file size. I took a 320x240 movie, exported 3:12 minutes worth at 15FPS as an image sequence to get 2880 frames, each of which in pict format was 220Kbytes, and then was able to import as a new image sequence with no problems. Well, let me reprase that. Minimal problems. The problems I had were that the numbers QT added when exporting as an image sequence contained no leading zeroes and so things got a bit out of order when I imported the sequence. But I didn't get the kind of error messages you are getting. QT created a movie file that played without any error messages.
You do have to be careful that the sequence number is the only number in the file name. Don't include a date or other number. Also, make sure the images to be imported in the sequence are in a separate folder that has no other files in it to confuse QT. It works best if the files are similar to this: image001.jpg, image002.jpg, image003.jpg, etc.