Cannot access PC shared external USB hard drive from MBP with Lion.

I have a PC on my network that has a secondary internal hard drive and an external USB 2.0 hard drive that are both shared on the network. From my MacBook Pro with Lion, I have no problem accessing the C and second internal drives, but cannot access the USB external drive from the Mac. I have no problem accessing the external drive from my 2 other PC's on the network. The external drive has the exact same sharing settings as every other internal drive on my network. All PC's are running Windows 7 and this is a home network. I don't have any servers or anything running. I just set up basic file sharing so that I can access any drive of any PC from any other computer on my network. The Mac just says "The operation can’t be completed because the original item for “T” can’t be found." when trying to access the external. Lastly, the Mac is on wifi, not ethernet. Thanks!

Update, So I disassembled the external hard drive case and pulled the bare drive out and connected the drive directly to my motherboard and without change any settings on the PC, the MacBook can now access it over the network. What is it about externals that the Mac can't access them over networks?