Windows drive mapping to IFS; DNS Nope, IP address Yes

Up until a few months ago, I had several working IFS folders mapped to
Windows drive letters, using the DNS address, i.e. \\
development.mycompany.com\transfers. All of a sudden, this stopped
working. I now get a dialog titled "Restoring Network Connections" which
says "An error occurred while reconnecting X: to
\\development.mycompany.com\transfers.
Microsoft Windows Network: The user name could not be found. This
connection has not been restored." No one else on my team is having this
problem. FWIW, we use Windows 7 Enterprise.

I *am* able to map a drive using the IP address, so
\\10.133.1.169\transfers works, although this makes it harder to know
whether this is the development server or the production server. Also,
I've found an odd behavior that, if I navigate to a folder below the root
folder of the mapped drive, Windows Explorer will return focus to the root
folder after some period of time, automagically.

My user IDs on both the Power i servers and Windows have not changed since
I started working here two years ago.

Our offshore service desk, to whom this has been assigned, is absolutely
worthless. After 50 days of waiting, including several pokes from me for
updates, I finally got an email from them today asking me to "confirm if
the issue has been resolved". As if the pixie dust fairy came in the
middle of the night and miraculously made this issue disappear.

So, out of exasperation, I am hoping someone here might be able to shed
some light on this. I am not a networking guy, so you may need to give me
explicit instructions *or* give me something I can pass on to our local
networking team that I don't necessarily need to understand.

TIA,
- Dan