B2 mage can't cast Life for a Life?

[thejeff]

I think mayusegems is the should test. There's something else for not enough gems. And I don't think that test even applies to blood mages? I've never seen blood mages just refuse to cast and all (almost) Blood spells use gems.

The -1 result for Life for a Life looks like what it usually gets when it can't find a valid target. Nothing should be immune and it's range 100, so that shouldn't apply. So it has to mean not high enough level to cast, but that doesn't explain why not to use the second slave?