DOORS trouble accessing databases on network drives

Answer

The reason IBM Rational DOORS has trouble accessing a database located on a network drive -- including a NAS drive or an NFS mount -- is because DOORS does not support having the database on a network drive

You can find this information in the DOORS server installation instructions.
For your reference, here is the language from the DOORS 9.2 install guide

... Enter the Port Number and the Data Directory
a.In Port Number, type the port number to be used by your Rational DOORS database server. We recommend you do not use a number lower than 1000.
The default port used by Rational DOORS is 36677

b.In Data Directory, type the path to the directory you want to use for your Rational DOORS database. This directory must be on the local machine and is where your data and user information will be stored. Rational DOORS does not support mapped drives for data.

c.Click Next

The same language is in the DOORS 9.3 Info Center:

Please reconfigure DOORS to use a local drive for the database.
Any drive that looks to the operating system (OS) as a local drive instead of a network or mapped drive is supported. Thus, SAN will work, if that is available to you, but NAS will not work, because NAS looks like a network drive to the OS. Please note that NFS mounts also look like network drives to the OS, so having the DOORS database on an NFS mount is not supported either

The DOORS 9.4 Info Center says:

If necessary, browse to a new data directory and click Next. This directory must be on the local machine, and is where your data and user information is stored. Rational DOORS does not support mapped drives for data.