Do the following to your original library:
Using iPhoto Library Manager to Rebuild Your iPhoto Library
1 - download iPhoto Library Manager and launch.>Click on the Add Library button,
2 - select the library you want to add from those in the selection window.
3 - make sure that in the rebuild window the checkbox "Scavange orphaned photos" is checked.
4 - now that the library is listed in the left hand pane of iPLM, click on your library and go to the Library ➙ Rebuild Library menu option
5 - in the next window name the new library and select the location you want it to be placed. Click on the Create button.
Note 1: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments. However, books, calendars, cards and slideshows will be lost.
Note 2: Your current library will be left untouched for further attempts at a fix if so desired.
If the newly rebuild library contains all of your photos (except for the last download) and works OK you can delete the first copy. Now you can download the photos from your trip photos again to the new, rebuild library.