Cannot open COM port in PHP - php

Question

I'm trying to open a COM port in PHP using the device's library file (file.dll) for the connection.
I get this error:
Fatal error: Uncaught exception 'com_exception' with message 'Source: file.DLL file.DLLDescription: com c:\users\user\folder\com.prg Error in line 9 OLE IDispatch exception code 0 from MSComm: The device is not open.. 1429' in C:\Users\user\folder\index.php:12 Stack trace: #0 C:\Users\user\folder\index.php(12): com->open(1, '115200,n,8,1') #1 {main} thrown in C:\Users\user\folder\index.php on line 12
The file 'com.prg' mentioned in the error does not exist in the folder (hidden files are visible).
I tried reinstalling MSComm, using another cable, using another port, reinstalling device drivers, updating PC drivers.
Here's the code:
<?php
$fp = new COM("file.dll");
echo "<br>". $fp->init();
echo "<br>". $fp->open(1, "115200,n,8,1");
echo "<br>". $fp->close();
?>
In open() command 1 - COM1 port, 115200 - bits per second, n - no parity, 8 - data bits, 1 - stop bits.
The connection works on another computer using the exact same configuration, so the problem here is not the code.
Any ideas?