You need to look at operator influence on locating the part especially if your program orientation is to the fixturing. Misaligning the part, while not causing a program failure, can still cause measurement errors.

Fixturing error can also be found by the way three different people use the fixturing. I have, for example, had problems with axial alignment of a cylinder because different pressures were used clamping it into a V-block.

Lastly small variations in parts can cause problems even though the program runs beautifully to the original part used in the original programming.

If you do not know how to run an R&R I believe that QS 9000 defines and gives procedures for doing so. If you also check the misc. forum you will find several individuals who can better help you.

Good Luck!

Jeff