Do you have this issue with multiple browsers?
Do you have all PHP warnings enabled, and do any show up in the logs/output?
What about if you replace line 79 with:

file_get_display_name( $v_filename );

(that still won't output the header, but at least traces the problem to either the header or the function call)

I have tried in Firefox 1.0.7, there is blank page as result. In MSIE 6.0 i got message "The page cannot be displayed".

PHP error reporting is fully enabled, and there is no runtime error. Header is translated right into:

Content-Disposition: attachment; filename="SomeFile.html"

Maybe this will help...

http://www.sweb.cz/fredy.c/pinfo.html

I think that this is an MSIE 6.0 bug. See http://www.faqts.com/knowledge_base/view.phtml/aid/4906 .

Fredy,

Is this still an issue in the latest releases?

Paul

Thank you for taking the time to report a problem with mantis.

Since this problem report was originally made, a number of releases have occured. Additionally no recent feedback has been received on this issue.
It appears that this issue has either been fixed, or may not be a relevant report for the current release.

Unfortunately you are not using the latest version and the problem might already be fixed. Please download the latest release from http://www.mantisbt.org/download.php

If you are able to reproduce this bug in the current release, or have some more information on how this feature could be improved in the current release. Please either change the mantis version on this bug report
to the version you tested and change the status back to "Open", or open a new issue report with more information.

Again, thank you for your continued support and report.