|We don't bite newbies here... much
Back in the "good old days", problems like this came up because COM5 and COM6 didn't have standard IRQ and port assignments.
But looking at the Win32::SerialPort docs, that doesn't look like it's the problem. W32::SP seems to expect to find the port in the registry.
I don't have a serial port on this box here, but do a quick search under \\HKEY_LOCAL_MACHINE\HARDWARE for COM1, and see if COM6 is defined there. (I hope that's where com ports would be...)
It's possible your other applications are finding it via "well known" IRQ/IO settings, and not via the registry.
If it's not in your registry, how to add it will depend on your version of Windows, unfortunately. Look for "Ports" in the Control Panel, if you're lucky.