The symptoms are very simple - you can add logos to the article or section in the private area of SPIP. But when you try to attach any document (image, file, mp3) nothing appears after you push submit button.
We detected this matter only with SPIP 2.1.x.
The reason - the empty table spip_types_documents in the SPIP MySQL database.
In this table are stored descriptions (MIME types) for most of file types. As I understand if SPIP could not identify the file it could not upload.
The solution of this matter is to copy the structure and content of spip_types_documents from any working website using phpmyadmin or mysqladminer.
Also I put the sql code as a single file. Sample SQL file SPIP 2.1.14 also can be downloaded here.
Change file extension to sql after you finish downloading.
Another matter solution could be here:
Cycling redirection on home page of SPIP website