Radius Persistence iRule error (bad field specifier)

It could be that the ${hsize} variable is being set to a negative integer. This could happen at the first binary scan the attr_len1 variable is being set to 0 or 1.

So if attr_len1 is set to 1, then hsize becomes '-2', because (1 -2) * 2 = -2.

Could you add an extra log line to your code to see what value is set to the attr_len1 variable?

when CLIENT_ACCEPTED {
 binary scan [UDP::payload] ccSH32cc code ident len auth attr_code1 attr_len1
 log local0. "DEBUG: attr_len1 = $attr_len1"
 set index 22
...