Have you installed or uninstalled any software just before the problem returned?

If so, your dll.xml file may have been rearranged and some other add-on is getting the port.

Andydigital knows more than I and he may check this post but here is what I do:

go to Users/....../apps data/roaming/microsoft/fsx/dll.xml

backup the dll.xml file

right click "edit" dll.xml file

I like FSUIPC near the top and less important items lower..

FSUIPC assigns the 1=com3 (or whatever)

That seems to prevent problems of the kind you have but I could be completely wrong.

Here is the XML file

<?xml version="1.0" encoding="Windows-1252"?>

<SimBase.Document Type="Launch" version="1,0">
  <Descr>Launch</Descr>
  <Filename>dll.xml</Filename>
  <Disabled>False</Disabled>
  <Launch.ManualLoad>False</Launch.ManualLoad>
  <Launch.Addon>
  <Name>Addon Manager</Name>
  <Disabled>False</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>bglmanx.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>Object Placement Tool</Name>
  <Disabled>True</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>..\Microsoft Flight Simulator X SDK\SDK\Mission Creation Kit\object_placement.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>Traffic Toolbox</Name>
  <Disabled>True</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>..\Microsoft Flight Simulator X SDK\SDK\Environment Kit\Traffic Toolbox SDK\traffictoolbox.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>Visual Effects Tool</Name>
  <Disabled>True</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>..\Microsoft Flight Simulator X SDK\SDK\Environment Kit\Special Effects SDK\visualfxtool.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>PMDG HUD interface</Name>
  <Disabled>False</Disabled>
  <Path>PMDG\DLLs\PMDG_HUD_interface.dll</Path>
  <DllStartName>module_init</DllStartName>
  <DllStopName>module_deinit</DllStopName>
 </Launch.Addon>
  <Launch.Addon>
  <Name>VistaMare Core</Name>
  <Disabled>False</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>VistaMare\ViMaCoreX.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>PMDG Options</Name>
  <Disabled>False</Disabled>
  <Path>PMDG\DLLs\PMDGOptions.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>PMDG Events</Name>
  <Disabled>False</Disabled>
  <Path>PMDG\DLLs\PMDGEvents.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>PMDG Sounds</Name>
  <Disabled>False</Disabled>
  <Path>PMDG\DLLs\PMDGSounds.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>Captain Sim Menu</Name>
  <Disabled>False</Disabled>
  <Path>Captain_sim\captain_sim.b757.menu.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>IvAp</Name>
  <Disabled>False</Disabled>
  <Path>E:\IVAO\IvAp v2\ivap_fsx_bootstrap.dll</Path>
  <Commandline></Commandline>
 </Launch.Addon>
  <Launch.Addon>
  <Name>Flight Recorder</Name>
  <Disabled>False</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>Aerosoft\Flight Recorder\AS-FlightRecorder.dll</Path>
 </Launch.Addon>
  <Launch.Addon>
  <Name>RAASPRO</Name>
  <Disabled>False</Disabled>
  <ManualLoad>False</ManualLoad>
  <Path>.\RAASPRO\RAASPRO.dll</Path>
  <DllStartName>module_init</DllStartName>
  <DllStopName>module_deinit</DllStopName>
 </Launch.Addon>
  <Launch.Addon>
     <Name>Just Flight TCAS Module</Name>
     <Disabled>False</Disabled>
     <Path>TCAS2v7.dll</Path>
     <DllStartName>module_init</DllStartName>
     <DllStopName>module_deinit</DllStopName>
  </Launch.Addon>
  <Launch.Addon>
      <Name>ICARO Menu Tool</Name>
      <Disabled>False</Disabled>
      <Path>ICARO\ICARO-MenuTool.dll</Path>
   </Launch.Addon>
  <Launch.Addon>
        <Name>FSUIPC 4</Name>
        <Disabled>False</Disabled>
        <Path>Modules\FSUIPC4_Loader.dll</Path>
    </Launch.Addon>
</SimBase.Document>

i must change now something? or what did you mean ?

 

I found the error. I install new hardware and i click accidentally to MCP so the MCP was inactive ...you must not understand this do not worry.