error when I try to fopen my COM1 port

Dear all,

I'm encountering problems with serial port in Matlab.

My code:

hSerial = serial('com1');
hSerial.Terminator = 'CR';
fopen(hSerial)

OCCASIONALLY, I get the following error:

=========

Error using serial/fopen
Open failed: Cannot connect to the COM1 port. Possible reasons are another
application is connected to the port or the port does not exist.

=========

Once this error appears, nothing helps, not even restarting Matlab, only rebooting the computer. I tried

delete(instrfindall)

which was no help.

To the best of my knowledge, no other instrument is communicating with the COM1 port.

Some facts about my setup:

• Windows 7 64-bit running on a Dell T3500 computer
• Matlab 2012b
• Serial port connected in series to several controllers (pumps, valve actuators...)

Many thanks!

Gilad Jacobson