Problem with Graph labels showing up as black boxes in Access 2010 Report when output as PDF

Hello,

I have an Access 2010 report that contains Microsoft Graph 2000 Chart Controls. When the report is opened, the graphs look fine. When I output the report to PDF using VBA's DoCmd.OutputTo with acFormatPDF, some of the labels in the graph are a black box.

Here is a screenshot of the graph when viewed inside of Access, looks OK:

And here is a screenshot of the graph when opened with Adobe Reader after it has been output as PDF:

In this example, the values are zero, but I've seen this with non-zero values. Also it is not necessarily every label, sometimes it is one, some, or all of the labels in series. Also have tried it on multiple computers with different hardware and get the same result.

Any assistance is appreciated, thank you.