I don't know when this problem started for me, but I can't seem to display most common file types from my DNN install.  For example, if I use the doc manager in radEditor to upload a doc, it seems to work fine.  But, when I click on the link generated, it says the doc doesn't exist (even though the path is correct).  I can put an image in the same folder and view it just fine.  Basically, it seems the only thing that doesn't generate a not found error are aspx pages and images.  I've tried zip, mwv, mp4,swf, docx, html, txt and they all produce a not found error.  I've tried different folders in my install as well. 

I made sure these are all allowable file types and that IIS has the MIME types defined.  Also, these files work fine on the same web server in a different website (non DNN).  And, I created a new portal with no content or modules added and the same problem exists. 

I am running DNN 5.6.1 and my app pool is .net v2

DNN 5.6.1 broke a number of areas as a result of changes made in the url rewriter / friendly urls / compression / domain alias providers.

Some of these have surfaced in the area relating to the serving of file types like .png and such - these bugs are largely dependent on which folder paths the files are located in.  One way to check if this is effecting you - is to look at your sites list of portal aliases - it maybe growing out of control with dnn adding new aliases for every file you are trying to access.

Westa