I fixed this in the repository. It will be in the next version.
As a workaround create a path which does not contain spaces it (in the full path, that means not in your user subtree). Then set the environment variable TMP to this path and start then Hugin:
set TMP=c:\TempPathWithoutSpaces
hugin
This can also be packed in a bat file and then Hugin be started with the bat file.
Alternatively you can also change the environment variable TMP in the Control panel, section users. This will also affect other program which are using the temp folder.