Recently we had this issue where after windows patches were applied, after a reboot the Sage Line 500 v7.1 Windows services no longer worked on our development and live servers. It was due to the Visual Studio dll msvcr71.dll being removed SYSWOW64 (32 Bit systems will be System32 and you can see in process monitor where the processes try to access the dll file and are unable to find the dll)

This can be copied back from a client Sage Line 500 install, as I found the dll was actually still registered

One possible cause I can think of is the registry entry for the dll in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SharedDLLs is set to 1, an installer upgrades a program to a newer version of Visual Studio and takes one away from the dll entry in the registry, where by it thinks it is no longer used and deletes the dll.