Thx for the hint,
Thx, I have done 2 rules which work well:
Rule1)
If (customers IS NEW OR customers.PasswordValidate WAS CHANGED ) AND LENGTH(customers.PasswordValidate)<6 Then
REPORT ERROR 'Password must be min. 6 characters'
customers.Password=customers.PasswordValidate
customers.PasswordValidate=UNDEFINED
Rule2)
If (customers IS NEW OR customers.PasswordValidate WAS CHANGED ) AND LENGTH(customers.PasswordValidate)>5 Then
customers.Password=customers.PasswordValidate
customers.PasswordValidate=UNDEFINED