I'm very new to Qgis so I would very much appreciate any help you can give me.

I have a point shapefile that corresponds to locations of animals captured. I've joined a table to this shapefile with additional information on each attribute, namely nb. animals caught in each point. I have another shapefile (hexagonal grid) and my goal is to sum the nb. animals caught for each point that falls inside each hexagon. In a preliminary search on the web, I found that maybe "join by location" could help me do this, but the problem is that I'm getting an "incorrect field name" error, for a field that doesn't even exist in any of the original tables and, on the other hand, it won't let me select the specific field I want it to sum..

Any suggestions? Is there any way I can do this without going into writing scripts mode?
Thank you very much.
Catarina