Establishing the PPPoE connection with controller there are few characters example '!', '@', '%', '^', '&', '*' working fine with these however '#' is also very common used characters which will be supported from 22.214.171.124 or 126.96.36.199 AOS before that it is not support.
Below is the test result from 188.8.131.52 AOS
(Aruba3600) #show ip pppoe-info
PPPoE username: #firstname.lastname@example.org