Hi Bonnie,
I have not used that audio plugin for a while, and with my poor memory, do not ever remember having a problem like that. I have switched over to using PoodLL for audio as the lead developer, Justin Hunt, has added capability to use it almost ANYWHERE in Moodle.
Just a couple of stabs in the dark. Based on your example, do your students get user names like that, that are used over and over each year/term by another student? When in college, I once had a programming class in which one "reused" user name did not get reset. (student0) The student who got assigned that user name coasted part of that semester because all the previous assignment files were still there, and he was dishonest enough to use them at first, until he realized the previous student as not an "A" student.
Have you tried "duplicating" the assignment and using the new copy while hiding/deleting the old one? I once had some "left over" data in an assignment once, and that was the quick fix that got me going again.
Hope this helps,
AL