it seems that somehow the attach disk action didn't finish or failed silently and therefore the VM is stucked in the HOTPLUG state. I'd try to do the following, look for the button for other actions and select Recover:
From the list of situations, you can try failure and then click OK. That should set the status of the VM to RUNNING and you would execute new actions again...
Now in order to debug what may have happened:
- Once you recover -> failure, the VM log may offer information about what command failed, if that is so paste it here to have a look.
- If no further info is displayed in the VM logs, it would be useful to have a look to /var/log/one/oned.log from the appliance CLI (ssh access as explained here) or from vOneCloud logs as it may give info about what is happening.
- Also from the CLI you could try to run oneimage show IMAGE_ID -x where IMAGE_ID is the ID number of the image you've tried to attach. You could paste the XML template here so we can have a look if it has something that may prevent it from being attached.
Let's see what can we obtain from the logs above...