The data types "%1!s!" and "%2!s!" are incompatible for binary operator "%3!s!". The operand types could not be implicitly ...

The data types "%1!s!" and "%2!s!" are incompatible for binary operator "%3!s!". The operand types could not be implicitly cast into compatible types for the operation. To perform this operation, one or both operands need to be explicitly cast with a cast operator.