RPM and the LPDSVC service
I have Windows 10 on my office computer, and I awoke this morning to find a new Windows version had been installed last night. I now have Windows 10 version 1607 OS build 14393.105, so that must be the one installed. Most people using our software, RPM Remote Print Manager, use it for receiving print jobs via the LPR/LPD protocol on port 515. If the Windows LPD Print Service feature is installed (and running), it conflicts with RPM's LPD functionality and prevents RPM from receiving print jobs on port 515. The LPD Print Service feature is not traditionally installed by default. Today, the Windows LPDSVC was installed and running and RPM was not receiving print jobs as it was the yesterday.
For most power users who know where to look, the fix is quite simple. Open the Services utility, locate the LPDSVC service and stop and disable it. Then, restart the RPM Remote Print Manager service and it should start "working" again. You can also remove the LPD Print Service feature using Turn Windows features on or off and restart the RPM sevice to accomplish the same goal.
Because I somewhat routinely test RPM together with the LPDSVC service, I can't say for certainty whether the LPD Print Service feature was installed prior to the Windows upgrade, but if it was installed, it was most certainly disabled. This indicates the update either installed it or enabled it, both of which are curious behaviors coming from a company poised to completely remove that feature from the operating system.