I have similar kind of problem.
I have a grid inside update panel. i have a functionality to export the data to excel using ExportToExcel.
After i have exported to excel, grid is refreshed by going to next page.
Now if i try to open a popup which fetches value from radgrid. Am getting null when i use get_masterTableView().
this works fine if i open popup without exporting to excel.
Any solution for this issue?