Logic can't find the instruemnts exs file. So you can choose to continue or find the file. More specifically it seems like it can't find certain notes.
The issue is that the EXS cannot find the samples themselves, NOT the .exs file.
To the OP:
1) Did you download and install all the additional content for Logic (including the Jampacks)?
If yes, you can check in the finder to make sure that the files are actually installed.
The ones you are missing should be in
Mac HD:Library:Application Support:Garageband:Instrument Library:Sampler;Sampler Files
Others could be in
Library;Application Support:Logic:Exs Factory Samples
If the files are on your harddrive, the issue could be with the Spotlight Index. Re-Index using this info: