Can you print the exact message you received?
I initially thought the issue could be that a password policy had been enabled on your switch but I can't replicate an error that says "password complexity".
Here is an example of a policy when it is enabled.
!
aaa password-policy mgmt
enable
password-min-length 10
!
(host) #show aaa password-policy mgmt
Mgmt Password Policy
--------------------
Parameter Value
--------- -----
Enable password policy Yes
Minimum password length required 10 characters
Minimum number of Upper Case characters 0 characters
Minimum number of Lower Case characters 0 characters
Minimum number of Digits 0 digits
Minimum number of Special characters (!, @, #, $, %, ^, &, *, <, >, {, }, [, ], :, ., comma, |, +, ~, `) 0 characters
Username or Reverse of username NOT in Password No
Maximum Number of failed attempts in 3 minute window to lockout user 0 attempts
Time duration to lockout the user upon crossing the "lock-out" threshold 3 minutes
Maximum consecutive character repeats 0 characters