multithreading and HTTP send

[edsuslen]

I am using multi threading per customer ( currently 2 only ) to send
http request for data pooling / pushing.
It looks like if one thread is in process of pooling data, the other
thread is waiting until that process is finished.

It takes about 20-25 minutes to pool file from 1st customer ( 1 big
file).
Meanwhile, second thread suppose to be sending responses for the 2nd
customer, smaller files, takes about 2-5 seconds to process, but it's
not processing them, until 1st customer's file is finished pooling.
As soon as 1st file is pooled, the other thread is quickly finished.

I am using simple threading:

Dim cls As New clsTimerThread
'Create the new thread
Dim t As New Thread(AddressOf cls.subRunningTask)
t.Start() 'Begin execution of the new thread

where clsTimerThread is calling my HTTP send class.

I need both processes to be able to work in parallel.
Right now I have a feeling of scalability issue.

Thanks in advance for any ideas.