Mailbox Locked?


Fark Lover
In the last few days, I've been getting an error almost daily from Mail (i.e. Apple's built-in mail program for X) that says something to the effect of:
<blockquote><font face="Verdana, Arial, Helvetica" size="2">

The mailbox {mailbox path} is currently locked by {username} on {hostname}. If you open a mialbox that is already in use, you may damage its contents.

[Open Read Only] &nbsp;&nbsp;&nbsp;&nbsp;[Quit] &nbsp;[Open Anyway]<hr></font></blockquote>
Something similar was happening to me with my bookmark file for OmniWeb in the Public Beta. Does anyone have any idea what's causing this and whether I'm ok to proceed in choosing "Open Anyway"?