Error message comes up after enabling !!!

I keep getting this error message after enabling the EasyCalcCheck PLUS plugin:

JCacheStorageFile::_deleteFolderJLIB_FILESYSTEM_DELETE_FAILED

Each time I enable the plugin this error appears on the front page of the joomla site.

I was running Joomla 1.6.6 and just upgraded to 1.7 and the error keeps occurring.

I'm hoping it might be a simple permission problem on a folder or file on the server somewhere.

All other plugins on the joomla site are working fine, and with no error messages, except for the EasyCalcCheck PLUS plugin's error message as reported here.

If anyone knows what is causing this, it would be greatly appreciated !!!

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