Sporadic issue accessing networked folders

Our office is on a small network. All users are on Windows Vista SP 2. I have been having an issue pop up irregularly for the last year or so and never really thought about it, but lately it's been bugging me a lot.

We have our "Documents" folders synced to the server for backup purposes. Occasionally I will lose the ability to access this folder. My shortcuts to files/folders in Documents will not work and when I try to access the folder through Network I get the following error message:

This issue appears to occur at "random" times although I am sure there's some reason for it. I'm not too network savvy and our small company doesn't have an IT person on staff (I'm usually the one to fix issues with printers/etc.). We have a third party guy that charges for service calls so I'd prefer to attempt a fix on my own.

Logging out and logging back in, as well as restarting, solves this problem and allows me to get into my folder. But when I'm in the middle of a task and I have ten windows open it's incredibly inconvenient to have to close everything and log out and back in.

Anyone have a suggested starting point? Please let me know if I've left out important information.

 

Is the server a real server, or is it someones workstation? If using a server, what OS is running on it. Also, what kind of equipment is being used for the LAN? Also, are all the users using Pro edition of Vista, or just Home?