I found that avsproxy_gui cannot open avidemux automatically when I pressed "create proxy button, and got this error instead.
(https://avidemux.org/smif/proxy.php?request=http%3A%2F%2Fs16.postimage.org%2F4nlv52qer%2Favidemux.png&hash=f10bb3ba22f5866d742da03d462d41f7521917b6)
Probably the same forward/backward slash problem as in http://www.avidemux.org/smf/index.php?topic=11351.0 (http://www.avidemux.org/smf/index.php?topic=11351.0) ?