Here is a revised version of the hotpot.php file. I've updated the zip file, as well, but haven't declared this to be a new 'version'. It's just a silent fix. For those who downloaded the module before this posting (Feb. 29), please just substitute this file for the current one in moodle/mod/hotpot/.
If you don't intend to use the JMIX module, there is no need to replace the file.