What is Incompatible?

Legal Definition
Two or more relations, offices, functions or rights which cannot naturally or may not legally, exist in or be exercised by the same person at the same time, are said to be incompatible. Thus, the relations of lessor and lessee of the same land, in one person at the same time, are incompatible. So of trustee and beneficiary of the same property. See People v. Green, 46 How. Prae. (N. Y.) 170; Co.m. v. Sheriff, 4 Serg. & R. (Pa.) 276; Regents of University of Maryland v. Williams, 9 Gill & J. (Md.) 422, 31 Am. Dec. 72.
-- Black's Law Dictionary
Legal Definition
Incapable of being performed by one person at the same time.
-- Ballentine's Law Dictionary