cache lookup failed for relation X

I found some posts be developers discussing this issue last Jan. and Nov.. See link below.
http://search.postgresql.org/search?m=1&q=cache+lookup+failed+for+relation&l=&d=&s=

But have not been able to find any suggestion on how an end user can use to get around this problem. Basically, we have a table X, trying to drop it would result an error message below:

cache lookup failed for relation XXXXX

I am using PgAdmin and I can still view the schema of this table, but any operation on it would get the above error.

Any suggestion on how to drop a table in this situation.

I am also wondering whether this problem has been fixed in newer PostgreSQL releases.

BTW, our postgreSQL version is 7.4.3.

Thanks.

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