(Seagate Go Flex wireless)
What is your iPhoto version? And your Mac OS X version?
With iPhoto '11 your iPhoto library needs to be on a drive formatted Mac OS X Extended (Journaled). Is your external drive formatted this way? If your drive is formatted differently, iPhoto will not be able to open the iPhoto library there.
When I drag the iphoto icon
And are you really trying to drag your photo library (from your "Pictures" folder) or your iPhoto application from the "Applications" folder? On MAcoS X 10.7 or later you will not be able to drag the application from the Applications folder.
I don't have a Seagate wireless drive; but I just looked at the manual.
I think you are supposed to drag single photo files to the 'drop files here' , not a whole iPhoto library. And I could find no information on the format of the seagate drive. iPhoto will not work, if the drive is not formatted MacOS X Extended.
Do you see your seagate drive as a disk on your Desktop or in the Finder's sidebar, or are you dragging to a well in an application window?