The string literal "%1!s!" contains an illegal hexadecimal escape sequence of "\x%2!s!". The escape sequence is not supported ...

The string literal "%1!s!" contains an illegal hexadecimal escape sequence of  "\x%2!s!". The escape sequence is not supported in string literals in the expression evaluator. The hexadecimal escape sequences must be of the form \xhhhh where h is a valid hexadecimal digit.