This is a shot in the dark since I don't have eyes on your system. I'm assuming you have 2 win7 computers with their own separate user accounts, not domain accounts.
You may have a username of Bob and even the same password on both computers, but it's not the same Bob as far as windows is concerned. One user account is actually something along the lines of \\comp1\Bob and the other one is \\comp2\Bob.
Since there is no domain security, comp1 can't add comp2\Bob as an authorized user.
Make sure your username and passwords are identical on both machines.
For ease of troubleshooting make sure that "everyone" has full control permissions. You must set this in two places. There are permissions on the SHARE that was created, this will default to 'read only' and is too restrictive. Change that to 'full control'. Next you'll need to check permissions on the actual folders/files that are giving you problems. Set "everyone" to full control on your music folder structure and tell it to update all subfolders.
If this doesn't solve it... here's something to try. As long as you're comfortable with editing the registry, you can't hurt anything. You'll be adding a new key, and if it doesn't solve your specific problem you can just delete it.
Run REGEDIT.EXE
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\WINDOWS\CURRENTVERSION\POLICIES\SYSTEM
Add a new DWORD(32-bit) entry.
Name the entry LocalAccountTokenFilterPolicy (case-sensitive, type it exactly)
Click OK
Double-click on the new entry and change the 0 to a 1.
Do this change on both computers and reboot both of them.
Hopefully you're back in business at this point.