Not able to connect to iMac via network!

Up until today everything worked great. I was even copying files from my Vista PC to an external drive attached to my iMac. I could see and share files across the network. This morning it all changed. I have made no changes to my system. I have repaired disk permissions, which really seemed broken. (I don't know why) Today I can still connect to my PC from my iMac, but I cannot connect to my iMac from my PC. I am receiving the following error:

imac is not accessable. You might not have permission to use this network resource. Contact the administrator of this server to see if you have access permissions. The remote procedure call failed.

I have never seen anything like this before. I have already checked my sharing settings and everything seems fine. Like I said it all worked yesterday. Today nothing.

I would appreciate some guidance here. Thanks in advance.

Any help out there??

exact same issue here, with xp

exact same thing, was working fine both ways, suddently can only view the pc from the mac, not vice versa. same error message as above. please help!

thanks,
kosh