- Are you running LEM 6.1.0? If not, what version are you running?
- Can you get a capture of the Fortigate Active Response connector you have configured under Manage --> Appliances --> Connectors?
- Does the config look correct?
- What model of Fortigate is it?
- What version of FortiOS is it?
The way the active response connectors work, it's looking for a certain series of prompts and sending a certain series of commands. If they don't match in some way or another, you can see the errors above. Chances are you'll have to file a support case and have the dev team dig in on this one, I'd guess something has changed in the firmware - OR there's a possibility that there are some options (like showing a hostname in the prompt, or requiring extra logins, or...) that might be toggle-able to make a difference in the short term.