Strange Occurrance

My company has many retail sites which access a centralized database over a wireless network. At only one of our locations, on 2 occasions, a custom ticketing application has produced a crystal report (v8.5) where the data is doubled. If you specify the same report the next day, the numbers are fine. Three separate reports are printed one after the other; the first 2 have duplicated (as in totals are exactly 2x what they really should be) and the third one is fine. The o/s is Windows 2003 Server; the database is SQL Server 7.0; the application is written in VB 6.0

Does anyone have an idea why this is happening? It is only one location and it happens very infrequently (2 times in the last 2 months).