PGSQL - WARNING: 25P01: there is no transaction in progress

Hello,

I have the following Warning with Postgresql, can anybody helps:

1- My server is crashing suddenbly
2- I do a cold reboot
3- In pgsql log, I have this message:
2007-04-27 14:15:05 EDT user database WARNING: 25P01: there is no
transaction in progress
2007-04-27 14:15:05 EDT user database LOCATION: EndTransactionBlock,
xact.c:2878
4- I try to search the transaction ID but can't find it.
5- How can I identify the transaction that caused this problem ? Is
there any log for the past transactions in PgSQL ?

I have found there is maybe two methods to correct the problem. It's
with ROLLBACK PREPARED or REINDEX but I'm not sure if it would work.

If someone can advice me steps-by-steps how to fix this error.

Thank you for your help.