MAJOR BUG? Network Authentication UNRELIABLE

Running 2011 Update 1 Build 6597 on Win7 64-bit O/S.

When trying to browse to network shares on a Vista computer, sometimes it works fine, other times (seconds later) it displays no computer names ot the computer name but no shares. And even sometimes you get all the way into the share and it displays no directories. And lastly I've got all the way into a directory and then the subdirectories are missing. It eventually prompts to enter the username and password again. I am 101% positive I am supplying the correct username and password. I go into Explorer and view the shares to make sure there is no problem on the network or destination PC and there isn't. It is inconsistent. Sometimes I can quit and restart the program and then I can see the shares again.

I've seen this issue posted several times by other users but not solution posted. Seems it may be a bug having to do with the latest update?

This is pathetic to have an unreliable backup program.