Access (occasionally) Denied to Network Printers across VPN

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The problem is the occasional loss of an application's access to a networked printer.  Rightly or wrongly, we have linked the probelm to the use of RDP sessions when the problem arises.  Perhaps you can explain why they are linked or suggest another cause of the problem.

Here is the scenario.  We have a hosted ASP.NET Windows 2003 application server which indirectly uses a third-party application (LabelG) to print to a networked printer on another Windows 2003 Server over a (RAS-based) VPN.  We understand that this is not a good idea, and have implemented FTP-based printing solutions for other parts of the system but, trust me, there are reasons why we have to use the VPN printer for LabelG.  And most of the time it works fine but occasionally, it returns an error stating that it can not access the networked printer.  It may be of use to let you know that LabelG is being invoked from a batch file which, in turn, is run every minute from the Windows Scheduled Task function.  The batch file runs in the context of an Administrator account, which we will call admin1.

The other thing you need to know is that we use RDP to manage the server, logging into the admin1 or admin2 accounts.  You will know that by default only two such sessions can exist at the same time.

Either through inspired brlliance or sheer coincidence, when we encountered the printer access problem, I logged one of these RDP sessions out.  Printer access returned and LabelG continued to print successfully over the VPN.  Since then we have had two more occasions when we lost networked printer access.  Each time, I logged one of the users out and printing resumed.

Is there a logical explanation for this behaviour?  If not, can you suggest a probably cause and solution?


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Rob WilliamsCommented:
What make and model of printer is LabelG ? I ask as I have seen similar with older ( 2 or 3 years) label printers. These printers use Kernel mode drivers which are actually not supported by Server 2003 and newer, due to security issues. A minor tweak does allow them to run. I mention this as I have seen a similar issue with RDP sessions. If one user is connected the printer works flawlessly. If 2 users connect the availability of the printer is very unpredictable, if a third user connects (full terminal server) the printer cannot be used at all.

If this is similar to your issue, I have no solution. It has to do with the kernel mode drivers and I spent a full day on it without resolving. Ultimately the solution apparently is newer printers with newer drivers.
davidxhareAuthor Commented:
Hi.  LabelG is actually a software program.  It  prints to a Citizen CLP521 printer.  Does this have a kernel mode driver?  Is there a tweak?
Rob WilliamsCommented:
I am not familiar with that printer. It certainly supports old enough O/S's to be a kernel mode driver.
You can install kernel mode drivers but I have never found a solution to allow stable multiple connections.
Sounds like you were already able to install the diver, however if not; There is no need to modify anything on Windows 2000 or earlier, and Vista and server 2008 will not allow kernel mode drivers, but on Server 2003 and XP you can enable installation by editing the group policy:
On a single server or PC:
Local Computer Policy | Computer Configuration | Administrative Templates | Printers | Disallow installation of printers using kernel-mode drivers | change to disable
Domain wide:
Default Domain Controller Policy | Computer Configuration | Administrative Templates | Printers | Disallow installation of printers using kernel-mode drivers | change to disable

To check whether a driver that you have installed is user mode or kernel mode, do the following:
-Click Start, and then choose Printers Folder.
-Click File, and then click Server Properties.
-Click the Drivers tab.
-Look at the Version column for a specific driver. If the version indicates Windows NT 4.0 you have a kernel-mode driver. If the version is Windows 2000, Windows XP and Windows Server 2003, you have a user-mode driver.

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davidxhareAuthor Commented:
Thanks for all the information.
I followed your instructions and the Version was Windows 2000.  So it would appear we have a user mode driver, and need to look elsewhere for the cause of this problem.
Rob WilliamsCommented:
Sorry David, I have no other suggestions. As mentioned the similar issue I had was with a receipt type printer. I had assumed it was related to the kernel mode drivers, but never verified.
Should you find a solution I would be curious as to the cause.
Good luck. (I will stay "tuned in")
davidxhareAuthor Commented:
I'll close this one down then.

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