PXE Cache
An oft troublesome “feature” of WDS is the PXE cache. This feature rears its head during OSD troubleshooting and testing and results in PXE boot aborted messages. Essentially, WDS lookups of systems in ConfigMgr are cached by WDS so that it doesn’t have to repeatedly query the database; items persist in the cache for 60 minutes by default. The known way to work around this issue is to adjust the timeout value of the cache in the registry at HKLM\Software\Microsoft\SMS\PXE\CacheExpire. By default, this value is 3600 seconds and reducing this value to something much lower, like 300 seconds should help during testing and troubleshooting scenarios.
Microsoft just release a new patch to address this issue: Operating system deployment fails in a System Center Configuration Manager 2007 SP1 environment if you deploy a different operating system to a client within one hour of a previous deployment (969113). Its not clear from the KB how the patch addresses this issue though, so I suggest downloading it to a test system and testing it out. When I do, I’ll post a follow-up.