Erase and snyc??

I used the Home Sharing feature to transfer music I purchased on another computer to my new laptop which worked fine. However, I then later tried to sync my iPhone on my new laptop, but I kept getting this message, "The iPhone "----------" is synced with another iTunes library. Do you want to erase this iPhone and sync with this iTunes library?"

I do not understand why this is happening! I have done this before and never had an issue until tonight.

If someone could please explain this to me I would really appreciate it!

Thanks!