could not truncate directory "pg_subtrans": apparent wraparound

Hi

got the following line at postgresql log:

May 16 01:17:35 xxx postgres[25550]: [1-1] LOG: could not truncate
directory "pg_subtrans": apparent wraparound

I assume this does not refer to xid wraparound? Should I be worried?

Database has only a few users and probably noone accessed it during those
hours. No other relevant lines were in the log, no crashes etc have occured.

postgres=# select version();
version

----------------------------------------------------------------------------------------------------------------------
PostgreSQL 9.0beta1 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC)
4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit

Regards

Mikko