I have now typed the matrix directly in the effect-string.
This works fine:
Code:

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float4x4 matScale1 = float4x4(1,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0);

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But with this:
Code:

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float mtlSkill1;

float4x4 matScale1 = float4x4(mtlSkill1,0,0,0,0,mtlSkill1,0,0,0,0,0,0,0,0,0,0);

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I get an error: "'matScale1': initial value must be a literal expression".