Opening a workgroup file that was created with an older version of Access is not so efficient. ie if it was built with Access 97 and you are using Access 2003.
How do you find this out?
Open Access 2000+, choose menu File then Open and navigate to the workgroup file. When it opens, if it says "You cannot make changes to the database objects in this database" then you have an old workgroup file.
To convert to a newer workgroup file is impossible, you have to recreate it from scratch as per this kb. http://support.microsoft.com/kb/824258
For that you are going to need the Name, Organization and ID that you used to create the original file. You are also going to need the PIDs of the usernames or you may as well stick with the slightly slower old workgroup file.
Now if that all sounds too difficult, you really want to ask yourself what you are doing with the workgroup file anyway. If you cannot rebuild a new one because you don't have the old credentials, then you may be leaving yourself open to difficulties down the track.
If you are running Access 2003 or less, you still can pick up my book on Access PROTECTION and security. http://www.vb123.com/map