You should be able to access the folder as
\\servername\sharename\foldername\newfolder
So do:
Directory.CreateDirectory(@"\\servername\sharename\foldername\newfolder");
You might have to check that the rest of the path Exists. If you want to
create more than one level of directories, i.e. \\hydhtc91670\mpIH\ is empty
and you want to make mpIH_deployables then make NewFolder_123 inside it, you
would need to create them in turn.
If this isnt the case, check the permissions on the share to ensure remote
users have access to modify and create folders.