I tried to repro, but could not (it worked as expected).
The function that is stated as missing (Composite.Search.SimplePageSearch.GetSearchResult) is a "External C# Function" and you should probably be able to see the definition of it below "Functions | C# Functions | Composite | Search | SimplePageSearch".
This definition points to a static C# method defined in the file "~/App_Code/Composite/Composite/Search/SimplePageSearch/SimplePageSearch.cs". Both the definition and the cs file was introduced when you installed the package.
My gut guess is that you are running on a site you have pre-compiled, and the new cs file is not "picked up" by asp.net, but thats just a guess.
Please the the server log (in the C1 Console, top menu Tools | Server Log) and see if there are any warnings or errors there. When Composite C1 start up C1 Functions (like this one that is missing) are resolved - any problems resolving a C1 Function is documented
to the log.
Let me know what you find out.