It looks like that Table 8.1 in that M5023n.pdf document shows the addresses in Hex. So that listing of 0x27 (hex) is actually 39 (decimal). If you are trying to read HR27 (which would be 0x1b (hex), that shows up as a N/A register in the table, so perhaps it is rejecting that request… Try HR39 and see if that works better.
FYI, in python you can do this to convert (you can do this in Script Console in the Designer as well):
