Did you convert the application to LabView 7.0 ?
I remember I had the same issue, same message when LV 7.0 was released, when I converted an application from 6.0 to 7.0
If I remember correctly, it was a bug in LV 7.0 converting application from 6.0 when a global vi was not converted first. The trick was to convert the global vi to 7.0, save it, then convert the rest of the application. The problem was fixed in 7.1