[help]having problem with Rss Feed

[imafia]

hello
This is my first post but i have this iissue for some days and help will be appriciated.
i addefd this code in >> myforum.com/forum/external.php

Code:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE rss (View Source for full doctype...)>
<rss version="0.91">
<channel>
<title>Triad Boiler Forums</title>
<link>http://www.myforum.com/forum/external.php?type=RSS2</link>
<description>This is a discussion forum for mySite. To find out about mySite Forums, go to http://www.mysite.com/forum/external.php?type=RSS2</description>
<language>en</language>
</channel>
</rss>

and change options from external data provider its showing rss tab on forum bar but when i open the link it shows blank page
any one have any idea
i didnt add or do any thing else so tell me if i should have to make another file or add more code in new file??

When i try to add rss feed in admincp from
On clicking preview i got this but can save it :

after save when i try to run rss schedulwd task I got this error :

and when i open rss feed link from forum home page i got blank page :

and runn rss post boot got this

but when i use other forum rss feed link it works fine and import posts on my forum
any idea how my forum rss will work?