VBA Error - Run Time Error 9 - Subscript out if range

When you get the error and click on debug, what line of code is highlighted.

Subscript out of Range errors from the Split function usually occur when the delimiter is not found in the text string and you then try and reference an array item that doesn't exist.

if the delimiter is not found then the Split function produces a string array with a single item, item(0) which contains the original string.

in this case I would guess your inner Split function does not find "'stats_chart_table_key'>" within .responseText; therefore there is no second item item(1), so when you try and reference that item for the outer Split function it causes an error.

also worth noting as a general point, the Split function always produces 0-based arrays, irrespective of if you have Option Base 1 set. although I don't think this fact has any bearing on your issue, just thought I'd mention it as useful info to know!