My library is too big for my laptop's hard drive.
I have it saved on an external hard drive, but every so often iTunes reverts to the c:drive of my laptop.
When I point iTunes back to the external hard drive location, iTunes doesn't recognize the library anymore.
How can I stop this?
Sounds like you might need to make a split library portable... With the library files on the external drive if the device isn't ready iTunes halts, you cancel, connect the drive, start iTunes and all is well, No preferences get altered.
Retrieving data ...