Hey, I just got this same message and I believe it started when I moved my wordpress install to a sub-folder. I am also trying to install the plug-in on another site, which ALSO is installed to a sub folder. I got an error message when I went to authorize the Add Link To Facebook Plugin saying that there was no index file (meaning it was searching in the wrong folder for a file).
To explain...for security reasons, I install wordpress into a sub-folder with a random name. Then, I pull the index.php and .htaccess into the main folder. From there I only need to modify the index.php so that it runs correctly.
I got this method from the Digging Into WordPress book, but am ready to ditch it as it has caused me countless problems with themes and plugins. So here's the question: Is it probable that this type of installation is causing the problem with the plugin??? And if so, is it possible to modify the plugin so that it will work???
I'd appreciate any type of help!!