If you have the Availability Engine enabled in your system, RCM now performs an availability validation when converting a quotation to an unallocated booking. 

A quotation can be converted in RCM using the "Convert to Unallocated" button in the following reports: Reservation Enquiry and Update, Release Quotation and Quote Management. When this action is performed, the Availability Engine will now run a check of all vehicles and existing booking, allocated and unallocated, to see if there is a vehicle available for this booking. At the time you click this button, if there are no vehicles of that category, at the quote's pickup location that are available during the entirety of it's duration, the following warning will appear:

If you select "No", the conversion will not happen and this will remain as a quote.

If you select "Yes", the conversion will happen, and the new unallocated booking will most likely be assigned as an ALERT booking by the Availability Engine, because there are no vehicles it can be assigned to. 

For more information on the Availability Engine, please see the Availability Engine Overview article.