Resolution:
Correct the code; then recompile.
Example:
In the following example, both the IMPLICIT and EXPLICIT operands use STRING as both the source and target type.
class-id A.
operator-id implicit (param1 as type A) returning ret as string.
set ret to param1::ToString
end operator.
operator-id explicit (param1 as type A) returning ret as string.
set ret to param1::ToString
end operator.
end class.