Ohh o.k. Is it only your machine that exhibits this problem? Or do other's have it also? If many computers exhibit the problem, then its probably due to a slow Browse Master Issue.
The Microsoft networking browser system consists of a master browser, backup browsers, and client computers. The Windows browse service maintains a list, called the browse list, of computers with resources (servers--a client computer can also be a server in a peer-to-peer network) in a workgroup. One computer, the Browse Master, maintains the browse list.
This Browse master maybe taking too long to serve up the List for the client PC's, such that Windows does not populate the Workgroup. You need to figure out which machine is taking over Browse Master duties and check for any irregularities.
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Ignorance is not necessarily Bliss, case in point:
Unknown has caused an Unknown Error on Unknown and must be shutdown to prevent damage to Unknown.