No order emails and blank page on order status change

[hisslink]

I have a problem with my orders. Shopper and vendor both don't get order emails. Also I get redirected to a blank administrator index when I update an order status. Also the shopper doesn't get the update email.
Other emails from the website do work (for example contactform).
These messages are in the Error log:

• ERROR vmError: getOrderStatusName: couldnt find order_status_name for
• ERROR vmError: The workflow for P or   is unknown, take a look on model/orders function handleStockAfterStatusChanged

Order statusses look normal to me (see attachment).

Does anyone have an idea what the problem could be?

Joomla! 3.4.8
VirtueMart 3.0.12
PHP version 5.6.17

[GJC Web Design]

did u search?

this has been discussed so often on here

tcpdf problems or lack of memory

[hisslink]

I tried searching based on the errors, but I didn't find a solution. Would you be so kind to tell me what to search for? Thank you.

[GJC Web Design]

https://www.google.be/search?q=virtuemart+error+update+an+order+status+site:forum.virtuemart.net