App Locking on Opening New Browser Window

[JJ_377]

I have these lines of code in my vb.net code behind (on load) of my
webform:

btnViewRequests.Attributes.Add("onclick",
"a=window.open('MainForm.aspx?LocationID = " & LocationID &
"','_new')")
btnReference.Attributes.Add("onclick",
"a=window.open('../RefFiles/Reference.htm','_new')")

If I do the following, the web app locks (hourglasses forever):

1. click on btnViewRequests and close the window that opens (which by
the way minimizes in the status bar from whence I have to open it).
2. click on btnReference and close the window that opens (this one
minimizes initially as well).

3. click on btnViewRequests again - THE BIG FREEZE! (the app locks up)

I have tried unearthing an error by putting breakpoints in, try-catch
blocks and inspecting the Event Viewer - no leads at all, can't even
get the code to run to a breakpoint because it never gets that far...

I note that if I keep the first new window open, no freeze occurs.

HELP!

My thanks!

J.

[JJ_377]

For the curious: I created a new html page from the legacy html page;
apparently, there was something in the original html page that caused
the problem.