juliapI'm not sure if it was set in the first place, so I set the variables in the Windows Environment Variables, and now it works!
Check to see what your HOUDINI_TEMP_DIR is set to, and make sure that it's pointing to a valid folder.
BTW, I tried setting the HOUDINI_TEMP_DIR in my houdini.env, but it does not seem to be recognized by the Houdini Engine.
I added the following line:
HOUDINI_TEMP_DIR = "%USERPROFILE%/AppData/Local/Temp/Houdini_temp"
Are you not able to set the variable in the .env?