This problem occurs when a Mac has more than 1 Gigabyte of RAM installed. Logic needs to see under a gig of free system ram.
To correct this problem, allocate whatever he has over the gig to Logic. For example, if you have 1.25 gigs of RAM, set Logic's preferred size to 250,000 which is about 250 megs of RAM.
This problem was fixed with version 5 of Logic.