Two things have you given Admin some resources and are you allowing Telnet on the management interface
see below for CLI
resource-class Admin
limit-resource all minimum 5.00 maximum equal-to-min
!
class-map type management match-any remote_access
201 match protocol xml-https any
202 match protocol icmp any
203 match protocol telnet any
204 match protocol ssh any
205 match protocol http any
206 match protocol https any
207 match protocol snmp any
!
policy-map type management first-match remote_mgmt_allow_policy
class remote_access
permit
!
interface vlan xx
desc management vlan
ip address xx.xx.xx.xx xx.xx.xx.xx
access-group input ALL
service-policy input remote_mgmt_allow_policy