I have a very special problem with my website.

It is in function since maybe three weeks.

For some people, it is working perfectly, while for some others, maybe
20%, there are problems.

These users can navigate in any page of my website, but they can't do
anything that requires server treatment, like do a research, connect
with their username and password, sign up, change language, ...

Their progress bar is just progressing very slowly, and finally they
get a time out error, or a DNS error.

I have been able to reproduce the problem by testing my site using
proxies. With maybe 30% of proxies I experience the timeouts problems.
Other website don't have these problems, even with the same proxies.

I have done many test pages to try to isolate the problem. If I reduce
a page to the minimum, like putting a label and making it change from
"Hello" to "Bye", the page does work.

But it is not easy to find the problems in my code. Some really basic
instructions can make that the timeouts problems happen, like :

            datagridPiece.Columns.Item(7).Visible = Not
Session("NoWebClient") Is Nothing
            datagridPiece.Columns.Item(8).Visible = False
            datagridPiece.Columns.Item(9).HeaderText = "Qté."
            datagridPiece.Columns.Item(9).Visible = Not
Session("NoWebClient") Is Nothing

On another test page, I am able to make one search, but not more, if I
want to search again I have to reload the home page.

I insist on the fact that the problem exists only for a minority of users.

Here is my website : http://www.promaxx.ca

Test pages :

http://www.promaxx.ca:8081/index.aspx
http://www.promaxx.ca:8081/test.aspx
http://www.promaxx.ca:8081/indexvieux.aspx

I can reproduce the problem with proxy : 202.138.141.46 port 3128

How could I solve that problem ?

Thank you.

I would try doing a tracert through the proxy : 202.138.141.46 port 3128

Get any *'s and you might have a net connection problem.
A router might be overloaded along the net somewhere.
This is why it would only affect a few customers because only their
pathway is overloaded.
Once the possible offending router is found try and contact the ISP
that owns it to address the issue.
It sounds like it is not a code problem since it works for the
majority of users even though it may still be a small possibility.  I
would try a tracert first and rule that out.

Thanks luxfestinus-ga,

I'm lucky, my dad is experiencing the same problems on his computer !
So I went to his home and made tests on his computer.

It is special that some parts of the code can be executed, and others
not. But it really seems a problem in a router somewhere. I tried
connecting through a proxy on my dad's computer, and then I was able
to search and do everything.

So : On a computer that works, I can connect through some proxy and
reproduce the problem. On a computer that doesn't work, I can connect
through some other proxies and make it work.

I will try doing a tracert through the proxy, and find the problem. I
am not very familiar with this, but I will just learn something more
:).

Thank you, I am not very familiar with Google Answers (firs time), but
if it solves my problem, I will get you to get the 100$ (well, 75% !).

Problem has been (somehow) resolved : 

I've disabled viewstate in my pages, and use session variables
instead. Too long viewstates, or some characters in my viewstates
variables seemed to caused problems with specifics servers or routers.

Anyway, just by setting enableviewstate="false" my pages now works
with ISP that caused me problems before.

Thank you.