Certain KMS clients won't activate

Question

Hello,
I work at a Community College where we have somewhere around 400 computers throughout the building. Up until this summer, we have been using MAK keys for our activation. However, to make our image deployment process easier, we have just deployed a KMS server
to handle our activation.
Our labs are slowly replaced over time, so pretty much each computer lab has PCs that were purchased in different years. I mention this because all of our newer batches of PCs have been activating just fine using KMS, but one style of PC which is a little
older fails while using slmgr /ato with no specific error. It just says
failed with an error, or something like that. No error codes or descriptive message. I also see no errors in the event viewer.
Our KMS server is running 2008 R2 Enterprise with a KMS host key. I know this is the right key as like I said, our newer PCs are activating just fine. I'll post a screen capture of the /dli output on our KMS server once
my account on here will let me. The current count is at 50 (the max it will display), it's status is licensed, and it's using a VOLUME_KMS_R2_B_channel key.
Our Clients are all Windows 7 Professional, and I am using one of the
generic KMS Windows 7 Pro keys with the slmgr /ipk command on those. Again, I know that's right because most of our PCs activated with it just fine. However, when running slmgr /ato on the failing clients I get that generic error.
Now our PCs are created via an image deployment, but I made sure to use the
/generalize option for sysprep. I have also verified that all other PCs created by this image have unique CMIDs or whatever the term is. I have even done a
fresh install from a CD on the PCs in question with the same result.
I have made sure windows firewall is off on these PCs, I moved one physical PC to a different area in our network to rule out some kind of network trouble, and verified several times that
DNS is hosting the KMS properly using nslookup.
We are all at a loss here, and I would appreciate any advice or suggestions on what else might be going on here.

Answer 1

Hello,
As I said in my original post, the PC I am currently testing is a fresh install from a CD in order to rule out any duplicate CMIDs. I am also able to telnet to the KMS server from the machine n question over port 1688. Just to rule it out,
I manually set the KMS server using slmgr /skms <hostname>:<port>. I still get the same error.
As for events 12288 and 12289, there are none under the application logs. The only event I see is under Applications and Services Logs > Key Management Services,
12290 which has a response of 0x0, indicating the request was successful. Still getting the error.
I have also determined that it is one specific set of hardware that is having the issue. We have around 60 of these PCs all the same model and they are the only ones having this error. And as I said in my first post, these boxes are spread
across almost our entire network, and I have verified that other PCs in the same subnets work just fine.