undefined symbol: SPI_plan_get_cached_plan

I am getting the following error when trying to execute a plpgsql funtion:

PSTERROR: could not load library "/usr/pgsql-9.2/lib/plpgsql.so":
/usr/pgsql-9.2/lib/plpgsql.so: undefined symbol: SPI_plan_get_cached_plan

This is on a SL6.3 system running postgres 9.2.2

We set this server up about a week ago, for migration tests from 9.1 to 9.2
After restarting the postgres service, the error went away. We've never
encountered this particular error
in any previous postgres versions (9.1, 9.0, 8.4) with our application.
I did not see any posted comments, regarding this error.

I looked through postgres 9.2.3 release notes but did not see any notes
regarding this issue.

Thanks,
Roger