You can find these files here:

http://www.dll-files.com/dllindex/index.shtml

The files that you all seem to be missing are dynamic link library files normally provided by Windows which are used by Avast.

Sometimes corruption results in the errors you are receiving, and sometimes a bad update causes the files to corrupt or become damaged.

If you download the files, don’t forget to register them using Regsvr32 function.
Good luck