Rebooting your computer(s) is critical. I've had this message come up in the past and a simple reboot was all that was required. On another occassion I had to uninstall, then reinstall the editor. I've also experienced this error when adding a PNG file to my PCF saved in Photoshop 5.5. For whatever reason adding a PNG file to my PCF that I saved in this version of Photoshop would cause the error. Once I got this error no PCF would download to the remote until I did a reboot. Of course if I choose to open my PCF in the editor again after rebooting the PNG file in question would need to be removed from my PCF first before attempting to download to the remote. I've since moved on to Photoshop CS. It's been clear sailing since then. The message will also come up if your PCF is too large to download to the remote which has happened to me more times than I can count.