If installing the older SDK worked, then trying to install an older AHP might work too.
If so, you can then try upgrading AHP, and seeing if it breaks again.
I know there was an issue with prior versions of the SDK installer, where certain files (the ahcmd.exe and ahscript.dll, specifically) were not being updated in the right locations.
If you had any SDK-created programs running while you tried to install or reinstall AHP, they might have locked the x10nets.dll, which may have prevented it from being updated.