ar_mailer intermittent SystemStackError

Hello! I am really hoping someone can help me figure this out. I am
hitting this intermittent error. It doesn't always happen when I am
doing a delivery action, but it happens sometimes. Its not always
against the same action (contactEmail) below, but I've seen it
sporadically across 3 other mailing actions. It's tough to reproduce,
but is definitely causing me some big problems!

Because the stack level is too deep, I feel like I'm not able to see
the entire error. If you can offer any ideas or insight, I would
greatly appreciate it!!

Rails 2.1.0
ar_mailer 1.3.1