Accessing a shared folder using other credentials with Windows 7

I was at a client office trying to connect to a shared drive on their network but was greeted by a

"you do not have permission to access" error!

Couldn't find any way to enter the required credentials as this message didn't had any other options. Tried to map the drive, selected the option to enter the correct credentials (with \\HOST\user) but it wouldn't work at all. The worst thing in all of this is that my coworker who is using OS X has been able to connect to that drive without any problem, he clicked on it, entered the credentials and could open the folder!

The folder is shared by a Windows Small Business Server 2008 machine.

The first rule to remember is that with almost all versions of Windows, in a single session, you can only be authenticated to a server with a single set of credentials. So if you already had a mapped drive, a shortcut on the desktop or something else, then you are already authenticated to that server.

One think you can do is drop down to a shell prompt, then use the command net use. The net use command all by itself will list your current connections. Use net use /delete \\server\share to delete any existing connections to that server. Once all your connections are gone simply use net use /user:username \\server/share. See the output of net use /? for more help.