One Workgroup computer wants Network Password

I have a small home network with three computers, Bravo, Delta and Harpo. All are running Win 7 Home Prem. x64. I'm using workgroup networking and all parameters are set the same. All are sharing drives D and F. All have identical user names and passwords. The problem is: Bravo can read and write to Delta and Harpo, Harpo can read and write to Bravo and Delta, Delta can read and write to Harpo but attempting to access Bravo gives a popup asking for a Network user name and password. No known user name and password works. I've tried a number of suggestions found on this forum (system time/date, security and sharing permissions (both set to everyone full control), etc. and nothing has changed. I've about pulled my hair out on this one. Any help appreciated.

After 5 days of constantly checking the shares the problem has slowly resolved to the point that delta is now almost never asked for a network password when accessing bravo. Nothing done in the last 5 days except occasionally retrying the share. From other posts in various forums intermittently asking for a network password appears to be an occasional quirk of Win 7 workgroup networking especially with Home Premium. No one seems to have found a reason or a fix.