Files sharing from Win98

I've been sharing files from my Win98 PC to my Win2000
laptop for some times now. Everything worked fine up to
yesterday, when i stopped seeing some folders on my Win98
PC. In fact, i can still see my PC in the network
neighboorhood, i can also see my sharing, and only the
first two folders a the root of the shared drive. If i
click on one of theses folders, i get a message saying
that the ressource is not available anymore.

The only thing that changed before it started to go wrong:

Defragmentation on the shared drive on the Win98 PC.
Installation on a VPN Client on my Win 2000 laptop.

Any idea.

Thanks in advance