ScalableList - Out Of Range error

I'm receiving this error (using SSRS 2008R2) in preview when looking at Page Preview, and when exporting to PDF.

In this instance, it seems to be coorelated with adding the "Page Break Before" option on a group. I've removed all "Keep Together" options from the report. How can I add the page break without breaking the report?

Thanks!

*** Additionally, the error reads "Index 0 is outside allowed range[0::-1]. that sounds like the 0 is in range, not out of range. What does this actually mena?