Strange DLLs loaded at runtime in VB.Net software

After a long time as a Java developer, I've switched to a position where I have to manage lots and lots of Visual Basic .Net code.

I've noticed lots of differences, but, probably, the one puzzles me the most is that in all the programs, when I run them, they seem to load lots of libraries (I think they're called assemblies in this context), and while some of them look like they are 开发者_高级运维just regular .dlls, most are just eight random characters named libraries.

For example, cut and pasted from the output window:

'RRHH.exe': se cargó 'c:\windows\assembly\gac\system.web\1.0.5000.0__b03f5f7f11d50a3a\system.web.dll', no se pueden cargar símbolos. 
'RRHH.exe': se cargó 'vq519j5h', no se pueden cargar símbolos.
'RRHH.exe': se cargó '7z7r342v', no se pueden cargar símbolos.
'RRHH.exe': se cargó 'dkuhznqg', no se pueden cargar símbolos.
'RRHH.exe': se cargó 'k-ggjvql', no se pueden cargar símbolos.

It's localized, it's says 'program': loaded '*', couldn't load symbols.

What are those? Why don't they have a name like the first dll?