Don't know if it will help you or not but I had that error until I set all the folders that the program writes to and all the text files to 777 on my site.
Also I don't know if it could cause it but if you used the auto loader to set up your site the Template folder and the HTMLeditor folders are empty. I had to download the auction zip file and FTP those two folders to my site. I'm surprised no one has mentioned it but then maybe I'm the only one who tried the auto loader because I have not done a lot of mods to my site yet.
Same here, I wasted some time with auto installer and after an hour i noticed template folder is empty. I will give it a try manually tonight. Hopefully it will work. Also I am not sure the templates are required to be in Default directory under template folder. When i downloaded the software, i found the templates are in default folder. Does anyone knows if the template folder has to be in default folder or in templates folder. This is the present format: cgi-bin\auction\data\templates\Default