First, make sure you have spoofing enabled, then change the spoof version to 3.65 Then try again.
If it still doesn't work. Open vitashell. Then go to the taihen folder and rename config.txt to something else (Add a letter or number to the file name)
Then restart the vita and go to go.Henkaku.xyz When henkaku installer loads, Press R button to FORCE INSTALL IT. After you do, it should work again. Go back to vita shell and delete the newly created config.txt file and then rename the old one back to config.txt (You renamed it cause force install overwrites with a default txt config file which may erase all setup plugins.)