AJAX an intrusting problum

i have used base tag in my site

like

<base href="http://mysite.com/sumsubfolder/etc/">


while making ajax request (i am using prototype.js)

initially it does not make ajax request

i have seen internaly the state

var state = Ajax.Request.Events[readyState];

is undefined

but magically it start working after a day

no one will bleave this word magically done

but i have seen this problem four-five times

ANY comments