When creating a Request, and associating assets with a truck (pickup, exchange, service, etc.) those assets must be valid for the truck you're using. Each truck has Valid Assets set for it, and only those assets will be allowed on that truck.
If you make a request for an asset, and it's not valid for the truck, then CRO will not let you dispatch the request. You must go into the Truck settings, for that truck, and add the asset type for the request into the, "Valid Asset Types" option.
Once the asset for your new request is added to the, "Valid Asset Types" option for the truck, and you save your changes, you will now be able to create the new Request.