Question : I get a 400 erro on HTTPQueryInfoA.

I issue HttpQueryInfoA on a file named on the server as %.jpg. I can't see any packets going over to the  server. Does this mean Windows is returning the error? The same code works if the file is more normally named.

Answer : I get a 400 erro on HTTPQueryInfoA.

Http error 400: Bad Request
This is because % is the escape character and .jpg is not a valid escape code.

Try %25 instead:

%25.jpg

will get the info of %.jpg