Can't map to second share on remote computer

On Windows 7, once you've authenticated against a server, you don't have to reauth for other mappings.

In fact, if you map a share to a drive letter, and then try to map a different share on the same server to a different drive letter, and then enter on the Map Network Drive dialog the same username and password used on the first drive mapping, you get this confusing error message:

The network folder specified is currently mapped using a different user name and password.

Despite the network folder not being mapped at all, and the username and password used not being different.

This baffled me for a while until I realized that once you have mapped to "server1" using those credentials, you can map to different shares on the same server without re-specifying the credentials.

(source)

Go to PC1 and inside D: > Properties > Security > Advanced > Owner - is the same as on C:, if not, change that.

If this does not help,
open cmd
Enter net use * /delete in the dos box

than try again

I've seen this before. Here's what you need to do:

Instead of mapping to \\PC1\D and \\PC1\E respectively, try mapping to the admin shares

The admin shares that you will want to connect to are \\PC1\D$ and \\PC1\E$. To do this, open Command Prompt, and type this (you could also save this to a .bat file on your desktop, such as connect.bat to execute at any time):

net use H: \\PC1\D$ /user:\\PC1\foobar 123456
net use I: \\PC1\E$ /user:\\PC1\foobar 123456

Simply replace H: and I: with drive letters you want, change foobar to the admin user, and change 123456 to the password of said admin user

You might have a spurious network share to \\PC1\D. This is easy to verify by entering into a command-line the command :

net use

If you see any other share in addition to \\PC1\E, which might even be that of the administrative share of D, just enter the command :

NET USE /DELETE \\PC1\share-name

You should now be able to connect to \\PC1\D without problem.

If this doesn't work, try to connect to <PC1 IP address>/D, entering the credentials as
<PC1 IP address>/user-name.