Oracle 10.2.0.4 huge amount of allocated commit callback headers (cmtcallbk) - has anyone experience

On our 10.2.0.4 database on windows 2003 we recently encountered a database access problem with ORA-12518 "TNS:listener could not hand off client connection", which was caused by the dedicated server process getting:

ORA-27300: OS system dependent operation:CreateThread failed with status: 8
ORA-27301: OS failure message: Not enough storage is available to process this command.
ORA-27302: failure occurred at: ssthrddcr

Metalink articles indicated this to be an resource problem with memory, but the database instance as well as the host had enough free memory.

But in v$resource_limit I found the allocated commit callback headers (cmtcallbk) to be 4 millions or higher (4 billions? Sorry, I didn't note the exact number, but is was very high, I assume it was the maximum long integer number)