The procedure entry point pango_font_map_create_context could not be located in the dynamic link library C:\Program Files (x86)\GtkSharp\2.12\bin\libpangocairo-1.0-0.dll
It looks like the libpango DLL for GTK it found is the wrong version and is missing some APIs. Did you follow the setup instructions, including downloading and installing the correct GTK version?
Hmm... the one referenced looks like a different (older) one. Maybe try dropping the libpango Cairo DLL from the tutorial directly into the SheepshaverGUI folder?
It seems you already have a gtk toolkit installed. The gtk toolkit linked to in our guide has a different version. If you already have gtk installed (in gtksharp) that version might be found by SheepShaverGUI. It then detects that it is not the correct version and give you the error you reported.
You can try to find all the .dll files in the gtk installation we linked to and place all of them besides the SheepShaverGUI program.
But you can also edit the sheepshaver_prefs file manually and set the required options.
Start with copying the content of you current sheepshaver_prefs file here.
You need to set at least (after adjusting for your installation):
disk C:\SheepShaver\MacOS90_1000
cdrom F:\
rom C:\SheepShaver\Mac OS ROM
ignoresegv true
ignoreillegal true