Why do I get the error 'Measure not applicable', when I use the created expression measure in KPI?

Why do I get the error 'Measure not applicable', when I use the created expression measure in KPI?

The reasons could be any of the following: Measure ID is not prefixed with Table Name. Expression is not correct. This error can also occur in newly created measures due to the following reasons: Measure is not created/defined properly. The character type is incorrect.