The same core code is used for loading geotiff in both the evaluation and the full versions. It must be something in your code. The best would be to have from you that geotiff to be sure where the problem comes from. I believe that some GeoTiffs requiere a world file (tfw) other don’t. With your Geotiff available we would be able to verify this. Thank you.
This is a known issue and has been fixed in 4.5.10.0, so please get the latest version (Development Branch) from helpdesk and have another try. Don't forget to add the following code like Yale suggested.
Internally within GeoTiffLibrary, we have 2 Lib types, Unmanaged and Managed. Only UnmanagedLibTiff supports embedded World file so we need to set the type to it.