I found how to fix for the insufficient space error by running the script found here. But when its time to mount the partition I get this error: "mount: Device or resource busy", anybody knows how to fix the problem? I already tried restarting the phone and reinstalling busybox.

EDIT: I did as user riiviin told me and ran this on adb/terminal emulator and now I can download big apps w/o getting errors, but you will have to run the commands again if you reboot because it will revert back to default cache directory.
umount /cache
mkdir /sdcard/cache
busybox mount /sdcard/cache /cache
Samsung Captivate (SGH-897)
Cognition5 v2 w/Launcher Pro