I trying to setup virtualenvwrapper in GitBash (Windows 7). I write the next lines:
1 $ export WORKON_HOME=$HOME/.virtualenvs
2 $ export MSYS_HOME=/c/msys/1.0
3 $
The error is saying that sh.exe (the shell) can't find a command matching mktemp, which means it's not present in GitBash, at least not in your environment.
One option is you could download a Windows version of mktemp, such as http://gnuwin32.sourceforge.net/packages/mktemp.htm and then place it in the C:\Program Files (x86)\Git\bin directory. The shell should then be able to match the mktemp command and be able to proceed.