If you have configured your Responder to manually select a signing certificate (rather than having the responder enrol by itself) and you have imported a certificate into the Machine certificate store. Everything looks good but your responder is still complaining with:

Bad signing certificate on Array controller

And taking a look in the event logs you are seeing:

Level: Error
Event ID: 23
Source: OnlineResponder
The Online Responder Service could not locate a signing certificate for configuration CA16 New OCSP.(Keyset does not exist 0x80090016 (-2146893802 NTE_BAD_KEYSET))

This could be a permissions issue

The Online Responder Service runs under the local NETWORK SERVICE account. It is this account that requires permissions on the key

Set the Permissions

1. Open a Windows Explorer
2. Navigate to:

%ALLUSERSPROFILE%\Microsoft\Crypto\RSA\MachineKeys

3. Select the key file from the list. Now, this may be easier said than done, as the filenames will be like this:

6687f9977771f049a15a9a5de0e17d82_8a8fdb36-f1a7-4fa3-bb7a-16297814b7a4
952203f4bd8a56ad04d5ba9ec9aab9c4_8a8fdb36-f1a7-4fa3-bb7a-16297814b7a4
...

You can sort by Date modified if you have an idea when you imported the key, or even re-import so you can spot the latest

4. Right click the file and select Properties
5. Select the Security tab (select Continue when asked, click Advanced if permissions are not shown)
6. Add the NETWORK SERVICE account (make sure you select the local machine as the From this location option – rather than your domain) and give it Read & execute permissions
7. Click OK to commit the change
8. Restart the Online Responder service