'operator' : no conversion from 'type1' to 'type2'
The compiler cannot convert type1 to type2. The conversion may not make sense because it violates C/C++ semantics.
If you encounter this error on code that was compiled with an earlier version of Visual C++, see Technote: Improved Conformance to ANSI C++.
Example
The following code has two conversion problems:
int i; char *p; int *j; const int *cj; void main() { p = i; // ERROR #1: conversion has no meaning j = cj; // ERROR #2: pointer to const obj }