I have found from personal experience that the problem lies not in the file being missing, but in Avast being unable to update the file during upacking.
This is usually due to the fact that Windows "stamps" the files as read only.
Do a system search for ALL dll files to locate the files msvcr70 and 71, and MSVCI70.DLL and MFC70.DLL
These files should be located in the C:/windows/system folder.
Right click on each file to display the dialog box. If either file/s are "read only', uncheck them.
Then do a manual update of Avast.