What the heck am I missing......

All systems Windows 10.

My home "server" has two physical disks, one is partitioned.

Disk 1:    C:  and  D:

Disk 2:  E:

I have shared E: with no problems, all files accessible from any machine on the network.

Shared folder Alpha on D:, no issues there.

Shared folder Bravo on D:, and from PC1 get the error "Windows Cannot Access \\server\folder\" - PC2 however can access the folder.

Permissions setup the same way as folder Alpha, same users etc yet PC1 refuses to get into it. 

Ideas ?