Sorry , I have got the version 1.7.15 !

I think the error is caused by the flash uploader. The flash uploader was newly introduced in the late Elgg 1.7 versions of Tidypics and was not really working well (I think some people still have problems with it using the latest Elgg 1.8 version of Tidypics).

I would suggest to switch to the basic uploader. You can configure the uploader to be used in the plugin settings of Tidypics so that you don't need to select the uploader on each single pics upload.