We assume here that you have installed a new 3rd party aircraft and want to add it to the aircraft library of FSXPilot.  
You get a message like that: 
Inline-Bild 1
.. and (in PRO) you cannot open the aircraft dialog window. 
That means that your third party manufacturer has forgotten an important parameter in the file aircraft.cfg of the specific plane or helicopter.
This parameter is called 'atc_model'. 
Some tweaking is required from your side, but its an easy task. 
Please open the file 'aircraft.cfg' of that aircraft (is in the FSX directory, folder "Simobjects" -> folder "Aircraft" -> folder "Your Aircraft")  in a conventional text editor and add the atc_model parameter in the [General] section (see below). 
Use a parameter name without spaces, in case  of a Bell 212 helicopter use Bell212

Save and exit.
Important: Restart FSX now or reload the plane in FSX !
Also restart FSXPilot. 
Upon the first start of FSXPilot, you may get a different warning message like: 
Inline-Bild 2
But you will now be able to (Shareware) add your plane in fspiklot.ini or (PRO) open the aircraft dialog window and define the parameters, after which the warning message will no longer come up.