Cache lookup failed for function 1 while enabling postgis onpostgres 10

I am trying to enable PostGIS on a PostgreSQL 10 database on Windows.
Earlier it used to work fine, but now I am getting an error 'cache lookup
failed for function 1' on enabling the extension.

I am using pgAdmin to do it and have tried shell also. I reinstalled PostGIS
from StackBuilder also.




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