[Boost-users] [asio] Error: should never be called

Since a few days I do get strange exceptions (boost::system::system_error) from my asio network code, based on v1.39. The message logged with .what() and .code() gives the following line: winsock: error: should never be called (error: should never be called:16646560) (The .code() output is put in parentheses.) I found two functions that produce the message in error_code.hpp (line 479ff) but I have no idea why they shouldn't be called. There's a comment to explain the implementation that refers to VC++ 8, but I have VC++ 7.1, so it doesn't seem that this code is called for VC++ 8 only. Are there any known cases, that produce this error message? thanks, Norbert