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Importing gerber data from older files is corrupting the drawing of arcs.

[QUOTE]Importing gerber data from older files is corrupting the drawing of arcs.[/QUOTE]

Gerber supports two types of arcs "90" and "360".  The first means the maximum arc angle can be 90 degrees while the other allows for a full-circle.   In many Gerber files (output from PCB CAD software) they do not follow the Gerber specifications and "explicitly" state which Arc Type should be used; and just assume the CAM software will guess it correctly.  By default FAB 3000 imports arcs allowing up to 360 degrees, but you can turn it off (limiting to 90 degrees) - that's all you need to do in this case.  See the following tutorial showing how to import your Gerber files.
http://screencast.com/t/m3gS1vUX

Note:  When the gerber data is "incomplete" there are certain times when FAB 3000 (or any other CAM tool) may guess wrong.  To be honest even engineers from other CAM software companies have downloaded FAB 3000 in the past to see how it handles "troublesome" gerber files, and we have done the same with their tools.  I wrote an article explaining the problems with incomplete gerber files:
http://www.numericalinnovations.com/pages/dont-trust-your-gerber-files

Here's another similar answer existing on the FAB 3000 forum:
http://forums.numericalinnovations.com/post/Problem-with-Gerber-Arcs-6218449?highlight=gerber+arcs