If deleting auc files helps temporarily, then I wondered if this problem was relevant:
daxmusings.codecrib.com/.../fixing-code-caching-on-ax-environment.html
blogs.msdn.com/.../identical-ax-2009-auc-file-created-for-multiple-ax-installations.aspx
But it sounds like one user, at least, does not fit this scenario, so that's probably no help.