Typically if ARCs are not loading correctly it simply means that you need to check the option: "Use 360 Degree Arcs as Default".
Why? The Gerber Specification has two types of arcs "Single Quadrant" (up to 90 degree arcs), and "Multiple Quadrant" (up to 360 degree arcs). The problem is that many PCB Layout tools do not pay attention to this clear difference of Arcs and generate gerber files with Arcs defined as "Single Quadrant" even though they are actually over 90 degrees. If these layout tools would simply reference "Multiple Quadrant Arcs (G75) when needed, there wouldn't be any problems at all loading gerber arcs (and thus no reason for this forum thread).
Numerical Support Team
Why? The Gerber Specification has two types of arcs "Single Quadrant" (up to 90 degree arcs), and "Multiple Quadrant" (up to 360 degree arcs). The problem is that many PCB Layout tools do not pay attention to this clear difference of Arcs and generate gerber files with Arcs defined as "Single Quadrant" even though they are actually over 90 degrees. If these layout tools would simply reference "Multiple Quadrant Arcs (G75) when needed, there wouldn't be any problems at all loading gerber arcs (and thus no reason for this forum thread).
Note: This actually results in an invalid Gerber file (actually about 50% of all gerber files generated by layout software have major violations or are invalid) but it's the job of a Gerber viewer to interpret & load those files as intended. Here's an article I wrote explaining this situation in more detail:
http://www.numericalinnovations.com/blogs/news/ensure-your-pcb-design-integrity-dont-blindly-trust-your-gerber-files
Thanks!
Simon