How can I fix a call to undefined function libraries_load() in GeShi Filter?
It appears you tried to use the recommended branch of Libraries API (marked green): 7.x-1.0. Generally, this is a good thing to do, but it can cause problems when modules have dependencies that are still in development.

In this case, Libraries API 7.x-1.0 doesn't the define the libraries_load() function that GeSHi Filter needs. You need to use the latest 7.x-2.x development snapshot.