How to fix error ASP 0201 on IIS 5.1?

Active Server Pages error ‘ASP 0201′
Invalid Default Script Language
The default script language specified for this application is invalid.

reinstall IIS
reinstall Scripting 5.6
re-register asp.dll
re-set Default ASP Language in Internet Services Manager
I’ve tried adding Language=VBscript at the top of the page
I’ve gone into IIS – the default language is VBScript – I’ve tried changing
it to Javascript and back again – no luck.
Tried re-registering the asp.dll and others, like scrrun.dll, just because
someone on the net suggested it.
IIS Reset – nothing
Installed 5.6 of the scripting engine

It was a permission issue (discovered using regmon).

I went to HKEY_CLASSES_ROOT and gave full permissions to IUSR on the script-related keys: vbscript, jscript, javascript.

Then I had to reset IIS and voila, the errors disappeared.