I'm having the same issue. I just sent Feedback to FileMaker.
Same problem. There appears to be no ability to format x and y axis labels - which is a big deal. Can not use charts for professional reports until this is fixed (or I learn how to do it). All of the online tutorials and examples I found have no axis labels - just vanilla text or numbers. Could you have to use a calculation field for axis label?
I ended up using Fusion Charts Free for Filemaker because of this problem. The reason I bought FileMaker Pro 11 was for the charts but they don't work as a runtime solutions. Some deal with FileMaker and whoever they licensed their charts from.
I can sell my FileMaker runtime with Fusion Charts and I don't have X or Y axis label $ format problems. Below is the link to their website.
Another alternative is a Web Viewer + Google Charts combo, depending on how you feel about Google Chart security..
I also upgraded to FMP11 for the charts, and was quickly disappointed by the lack of complex charting functionality and options. I wasn't expecting them to do everything Excel can, but even simple features like data labels for bar graphs are missing. I'm hoping the charts feature is vastly improved in the next iteration of FileMaker. Dynamic database-driven charts are very handy!