Project Server 2013: Can’t save a Resource in PWA

When trying to save a Resource in PWA, you get the message:

The resource could not be saved due to the following reasons: A resource availability contour cannot go outside the range of the resource’s earliest and latest availability dates.

2015-06-15 16_49_12-Standard - ASG-Remote Desktop 2012 - __Remote
When you open the Resource in Project Professional 2013 and have look at the “Resource Information”, the “Resource Availablity” under the “General”-Tab looks quite strange, like this:

2015-06-15 16_14_51-Standard - ASG-Remote Desktop 2012 - __Remote