Network Share of My Book Elite 2TB and My Book 500Gb

I have 2 WD External HDDs in the form of a 2TB My Book Elite and a 500Gb (Old) My Book. Both are attached to a PC running Windows XP Pro SP3 with all the latest patches.

I have shared these drives along with another internal HDD of the computer across the network. I achieved this by using the Share tab within the properties dialogue of each drive.

The internal HDD can be seen and accessed by 2 other machines on my Network (one running XP Pro SP3 via a wired connection, another running XP Home SP3 via a wireless connection), however although the two WD External HDDs are listed when I attempt to access them I get an error message telling me to check with my Network Administrator.

Any thoughts on why I cannot access these drives?

Thanks in advance everyone