I wasn’t going crazy… I finally tracked it down.

Problem:
I was stress testing a new application by submitting lpr.exe jobs from windows clients using lpr.exe I tried it from:

• Windows 7 Ultimate 64 bit
• Windows Server 2008 (32 and 64bit)

Using a windows batch file:

@echo off
for /L %%i in (1,1,25) do ( 
	echo %%i
         rem Use ping to put a delay in
	rem ping -n 1 -w 5000 1.0.0.1
	lpr -S 10.11.12.13 -P printqueue print_this.txt
)

The jobs would freeze as it appears now at the 11th job.

I was seeing Event ID 4227 http://technet.microsoft.com/en-us/library/cc735929(WS.10).aspx in the lpr.exe client System logs

Cause
The cause is the "LPR Port Monitor" that you have to install to get lpr.exe has an LPR RFC limitation re: http://support.microsoft.com/kb/2003449

Resolution
On each client I added the following to the registry and all of a sudden I can submit 25 jobs as quickly as formtrap can receive them.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\LPDSVC\lpr]
"UseNonRFCSourcePorts"=hex:01