Not without more information - what happens - what errors do you get - if the external drive formatted Mac OS extended (journaled)?
This procedure has been used thousands of times successfully
Moving the iPhoto library is safe and simple - quit iPhoto and drag the iPhoto library intact as a single entity to the external drive - depress the option key and launch iPhoto using the "select library" option to point to the new location on the external drive - fully test it and then trash the old library on the internal drive (test one more time prior to emptying the trash)
And be sure that the External drive is formatted Mac OS extended (journaled) (iPhoto does not work with drives with other formats) and that it is always available prior to launching iPhoto
And backup soon and often - having your iPhoto library on an external drive is not a backup and if you are using Time Machine you need to check and be sure that TM is backing up your external drive
Thanks for reply. The external drive is formatted for Mac OS. I just tried to drag and drop a single image from the desk top and it would not work. I looked at the information of the hard drive and it says, 'read only' in the system info, sharing and permissions. Could this be he problem?
In regards to Time Machine, where is a good location within the system to use for Time Machine backups?