Inspiron serial port problem

I have purchased a computerized telescope that has the capability of interfacing with a computer. 

 

When I connected the telescope to my Inspiron 5000e the first time, it worked fine.  When I tried later, the computer could not find the telescope.

 

I contacted the telescope maker and asked about the problem and the first question they asked was "Are you running a Dell laptop?"  When I answered yes they informed me that the Dell serial port transmits extra nulls through the port and those signals confuse the telescope's computer and it refuses to communicate.  They suggested I try to find a serial port upgrade.

 

The serial port works fine with everything else but I can't seem to find a serial port driver to fix this problem.

 

There was a link in a message to a thread addressing this problem but the thread has been deleted.

 

Can anyone help me with this?