Here are the CLI commands for enabling TACACS on the S3500/2500. You will need to create the matching device on the ACS server as well.
Creating mgmt auth is not supported in webui.
aaa authentication-server tacacs "CORP"
aaa server-group "TACACS"
aaa authentication mgmt
To trouble shoot please enable following loggings
#logging level debugging security process authmgr
#logging level debugging security subcat aaa
# logging level debugging security
# show log security 100