Solved
Prime tries to turn your VLL squared over the angle 30°/S3phi, and with S3phi bearing a power unit, that results in a unit error: The unit deg/W is not compatible with an angle. Now Prime isn't very careful with pointing to the right spot of an error, so you're getting a somewhat cryptic error message. Here's the same situation:
If you put brackets ( and ) around the polar conversion it works.
Or rewrite:
Which also indicates that you should be cautious with the other expressions involving that polar conversion operator:
Success!
Luc
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