Debugger stops "can't find source file", even with "step over"

Hello Forum,

I' using SSP 1.3.3 and S7 MCU, I had a small but working hhtp server application, web content started from usb mass storage.

But since a few days I always get the following debugger message (sse screenshot below) even if I want to step over the function call or place a breakpoint right after the function call.     USB media works without problem because I can read the volume name before calling fx_file_open().

    /* return requested resource or query */
    if(strcmp((const char*)resource,(const char*)"/index.html")==0)
    {
        fx_status = fx_file_open(p_eth->http.cfg.pv_fx_media, &fx_file_html,(CHAR *)"index.html", FX_OPEN_FOR_READ);

            if (fx_status != FX_SUCCESS)
            {
                tx_thread_sleep(TX_WAIT_FOREVER);
            }

   ......

}

I'm not sure whether I've changed something unintended in the project/debugger settings, or what ever could have happened?

Any idea or help, is very appreciated.

Thanks in advance and best regards

Ralph