what is with the vcache file in the os?

i have a e-machine, 550 monster. when i got it, there was no command under vcache in the system.ini. support gave me this,maxfilecache=8192 on one line and chunksize=2048 on the other.that is with 192 megs of memory.i up-graded to 256 megs and now iget fatal error in vcache. does up-grading memory change every thing in this file?