Yes, I just tried the file manager and got the same error:
The File D:\Source\3_EVO\WEB\HRGPortal\iSuite_v2.2\Portals\0\Rc test.pptx Is A Restricted File Type. Valid File Types Include ( *. swf, *.jpg, *.jpeg, *.jpe, *.gif, *.bmp, *.png, *.doc, *.xls, *.ppt, *.pdf, *.txt, *.xml, *.xsl, *.css, *.zip, *. pptx, *. ppsx, *. docx ). Please Contact Your Hosting Provider If You Need To Upload A File Type Which Is Not Supported.
I am running DNN v4.9.4 if that is any help (an upgrade to V5 is not an option at present).