This race class combo is not allowed?

[_gunthar]

I created a player character, and at the end, I got this error: This race class combo is not allowed. Where do I see what is allowed?

Edit: Tried a different race and class combo and it happened the same error again.

[Rtha]

The charplanner tells you which race+class combinations work.
Also note that Valkyries can only be female.

[_gunthar]

First, I tried a Highlander friar, but nope. Then, I wanted to create a Frostalf bonedancer, but that was not available either.