Type Mismatch on referring php file instead of xml file

Hi
Earlier i was using like the code mentioned below i.e. i am giving reference to xml file which works perfectly.

conn = CreateObject("roAssociativeArray")
conn.UrlPrefix = "http://webserverIP/roku/"
conn.UrlCategoryFeed = conn.UrlPrefix + "/show001.xml"
conn.Timer = CreateObject("roTimespan")
conn.LoadCategoryFeed = load_category_feed1
conn.GetCategoryNames = get_category_names1

Now i want to make it dynamic by referring php file which will internally generate xml file as shown below where showSelection is the interger id of the show which is selected on the screen.
conn.UrlPrefix = "http://webserverIP/roku/"
conn.UrlCategoryFeed = conn.UrlPrefix + "/showname.php?id="+showSelection

When i check the o/p of both the file in browser, there's is no difference in the o/p file. The xml file content generated by php code is the same as the earlier referred xml file. But it is giving the error of Type Mismatch.

Kindly help how to solve this error.

Thanks
Amit