Thamks for all the above replies -they are appreciated.
This post was originally raised because I had an order which was changed to "Cancelled" somehow or other. This was not done by admin. The same order also generated the common error "An error with your payment method Paypal on your store ****** Shop. The details are logged in the file paypal.3.log.php - the Vrtuemart Team". Whether the two are related, I do not know. However, the normal payment was received in the relevant Paypal account and an email from Paypal notified of the receipt of the sum.
I then spent some time reading various forums to try to understand, unsuccessfully, what had happened. I came across posts such as this on the Virtuemart forum:
The functionality to create conditions for order cancellation is provided to admin.
The conditions of cancellation are based on four scenarios. Firstly on order price where admin needs to set a minimum amount for the order to be canceled.
The next scenario that has been given for cancellation is the time duration which is customisable up to the day, hour and minutes of order.
The third most scenario that has been provided is according to the status of the order.
The last scenario is on the basis of products.
The configuration of Email templating for both admin and buyers is available.
Easy to configure and handle at admin end.
Allows registered/guest users to cancel their order.
I then realised that I did not understand how order cancellation should be set up and raised my original post.
Any further comments appreciated.