QextSerialPort - very strange problem with runtime

[code_err]

I've used this library before and didn't have such a problem. I did the same things as always.
After adding line which opens COM port: port->open(QIODevice::ReadWrite)
my program can be compiled but i get this message

Clipboard02.jpg

I use dynamic linking, i.e.

in my pro file have this:
LIBS += -lqextserialport1
in my sources include header file from library and in build directory have .dll.

Spend over 5h and can't understand why it happens. When i wrote simple, testing app everything works. Maybe there is a conflict because of using dynamic linked Qwt and QExt?

My compilator is MinGw-gcc4.4.0, Qt4.8 on Windows 7

I can add that i use version 1.2 of QextSerialPort, creating QextSerialPort object on heap doesn't make any runtime problem, just opening is not working. All libraries was compiled in MinGw in Qt4.8