Building under Haxedevelop fails

I've got the following error (similar for hxcpp and hxcs) for default projects in C++/C#.
OS Windows 7 x64.

Running process: C:\Program Files (x86)\HaxeDevelop\Tools\fdbuild\fdbuild.exe "E:\temp\New Project14\New Project14.hxproj" -ipc 7de8e6ea-dcd6-4496-acea-c62337a09d79 -version "3.4.0" -compiler "C:\HaxeToolkit\haxe" -notrace -library "C:\Program Files (x86)\HaxeDevelop\Library"
Building New Project14
haxe -cp src -cpp "E:/temp/New Project14/bin" -main Main
Unix.Unix_error(21, "open_proc", "haxelib path hxcpp")
Build halted with errors (haxe.exe).
Done(1)

hxcpp and hxcs are installed. System environment variables are set.
HAXELIB_PATH=C:\HaxeToolkit\haxe\lib
HAXEPATH=C:\HaxeToolkit\haxe
HAXE_LIBRARY=C:\HaxeToolkit\haxe\std
%HAXEPATH% is appended to PATH variable value.