RMAN backup error

When I run my RMAN backup script I get the following error:

RMAN-00571: ================================================== =========
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ================================================== =========
RMAN-03007: retryable error occurred during execution of command: backup
RMAN-07004: unhandled exception during command execution on channel dev1
RMAN-10035: exception raised in RPC: ORA-19504: failed to create file "/db01/app/oracle/admin/train/adhoc/TRAIN_DB_05nsjjn2"
ORA-27044: unable to write the header block of file
Linux Error: 22: Invalid argument
Additional information: 2
RMAN-10031: ORA-19624 occurred during call to DBMS_BACKUP_RESTORE.BACKUPPIECECREATE

RMAN>
RMAN-08031: released channel: dev1

Recovery Manager complete.

I definitely have enough disk space:
/dev/sdb1 247G 143G 91G 62% /db01

I am mostly curious about the "Linux Error: 22: Invalid argument" line. Has anyone come across this before?

I am a sysadmin trying to troubleshoot this for our DBAs so please forgive me if I left out any pertinent information. Thanks.
-K