Curosor locking up in form

Does anyone have any experience with their cusor locking up in a form.  We are having sporadic issues where it's a handful of users and on different types of forms.  They can be working away entering transactions (and/or scanning them in) and then all of a sudden their cursor locks up or gets stuck.  They cannot click out of that field.  They are, however able to tab through, but for the most part, they need to click several fields away so tabbing isn't really helpful.  The only thing that works for the user is to close out the form and