I see you have two problems.
1. Generating RTF report
There can be more reason of error message “Access denied…”. Typical case is, when you have open file “<file_path\filename.rtf>”. To solve this problem please close application that has open rtf file, or set output file of report to another.
Another reason can be, that file “<file_path\filename.rtf>” is present on HDD and it is readonly.
2. Exporting model to image
Unfortunately you didn’t write version of your TDM and type of output file(png, bmp, jpeg). If you provide us your version we will do some test.
But I think, that this message you can get, when diagram is to large to export. I don’t know how many entities and other objects is present of your diagram. There is some trick how decrease size of generating image(Switch of Gradient Effect, Switch of Display Key Graphically, choose low pixel format) or work around is print it to PDF.