Back in the good old college days of punch cards and standing in line to hand those punch cards to a surly operator, when there was a typo on one punch card, you didn't get a wonderful wireframe perspective, you got twenty pages of erroenous error messages that talked about everything but typos, since professional programmers never make typos.
These were pocket protector days.
Punch cards were funny. Guys carried their projects in long cardboard trays. Getting into cars, you'd store your coffee and punch cards on the roof while you thew your book bag into the backseat of the carpool car and then forget. Guys would be driving home, a stream of cards dancing out and up behind the car, landing in spilt coffee.
When you see an error message, all you can be sure of is that something is wrong - it could be a program error or a file corruption - who knows? Who cares? Merging makes ArchiCAD re-read the data and somehow it gets reorganized. I learned this trick beta testing some software where you could never re-open a file because of some wierd issue. Merging would work, tho.
It helps to know voodoo.
Dwight Atkinson