Why can't Veterans and Military Hospitals share Computers?

The VA Medical Centers use a system called CRPS or CPRS (I can't remember which) and the Military use CHCSII. These Computers can't share information. The system the VA uses makes it practically impossible to make a Medication error. In fact the only way a Medication error can occur is when the Nurse preprints the Medications list and passes her Meds by that instead of using the arm band on the patient and the Computer to pass the Medications. It's not to say that the Doctor can't order something wrong but there are checks and double checks that can make that less likely.