If you go to the build window and put the cursor on that '?', what does it show in the status line at the bottom of the editor window for the character code? It will be the box to the right of the one that says something like "CRLF ACP".
Edit: actually, that previous paragraph only works if you have the build window sent as a editor window, not in the build tool window. Instead, select that ? character, copy it, and paste it into a scratch file, and then put the cursor over that and see what the character code is in the status line at the bottom of the window.
Also, if you open up your project (.vpj) file for the project you added the make tool to, if you find the <Target> tag for make, does CmdLine attribute of the Exec tag look correct, or does it have any leading characters?
I scanned over the code that generates the commandfile referenced in the vsbuild command line and I don't see any obvious bugs, but I'll take a closer look in a few minutes.