I got the same error right after the rev 18 install. I believe it has to be a compatibility issue between the new rev and old wad manager.
I updated hermes 222 v5
and ran the wad manager 1.5 via 222 instead of 249..
This allowed me to install new wads. I hope this works for you.
Try uLoader(2.6 and 2.7) use cIOS 223 with IOS37 merged with 36 and see if that works. I was told that the new version of usbgecko will work too with cios rev 7 or higher, but I haven't tested this yet.