Going to try Seattle tonight to see if it's consistent.

I found a way to fix this issue and prevent you get an FSX crash although this "fix" will not prevent from having tjhis type of failure message. The fix is just intended to let you continue flying online without an FSX crash.If you are flying online and got the dreaded pop-up message, DO NOT CLICK on any of the pop-up options. First disconect Squawkbox and then QUIT (Close) Squawkbox. Once the Squawkbox is gone, click on the IGNORE option on that pop-up window (Right option). It will close the pop up window.Give the sim a few seconds and it will run nicely again although maybe it will be initially paused. Then inmediately start Squawkbox again, connect online and keep flying online like if nothing has ever happened. Chances are the pop-up message is not showing again on this flight. If it does, simply repeat the procedure.As I said, it is not a solution to PREVENT this happens but at least it is a solution so you do not lost your flight mid-air by a FSX crash.Hope it helps

I found a way to fix this issue and prevent you get an FSX crash although this "fix" will not prevent from having tjhis type of failure message. The fix is just intended to let you continue flying online without an FSX crash.If you are flying online and got the dreaded pop-up message, DO NOT CLICK on any of the pop-up options. First disconect Squawkbox and then QUIT (Close) Squawkbox. Once the Squawkbox is gone, click on the IGNORE option on that pop-up window (Right option). It will close the pop up window.Give the sim a few seconds and it will run nicely again although maybe it will be initially paused. Then inmediately start Squawkbox again, connect online and keep flying online like if nothing has ever happened. Chances are the pop-up message is not showing again on this flight. If it does, simply repeat the procedure.As I said, it is not a solution to PREVENT this happens but at least it is a solution so you do not lost your flight mid-air by a FSX crash.Hope it helps

This works for me as well although I don't have to quit or disconnect SB. I've tried running SB in a separate window with no luck. I received an error message that completely closes SB out no matter the response. When running SB through FSX, as long as I click on Ignore when I receive a C+++ Assertion error, I'm good. But the error window always pops up when another pilot or controller online contacts me through chat. I've experienced SB error pop ups on other occasions as well, especially in an area with lots of online traffic, and as long as I keep clicking Ignore, it works. But you have to be on it, because it looks like the sim freezes until you react to the message. If anyone wants to correct me if I'm wrong, please do, or if you've had a similar experience, please share it. Really hope this issue can be worked out.

High,SB4 works fine in FSX but you have to use it in a window mode (outside on its own)and FSX as well, this is a drawback.Now I use it for FS9 only.Now that I have Fsinn sorted for FSX the biggest advantage is once everything works fine I put it in full screen and I get 50 pc more FPS...AlainV

Ok, I found a permanent fix for this absurd issue. And it is really absurd and simple.Simply bring power to your aircraft, thus powering your radios. I use to change the VHF 1 to UNICOM 122.8 and AFTER this is done I launch Squawkbox as as external application, connect and voila, no more troubles.Nice and smooth.I have not had any troubles with this since I am using this method.So make sure you have your airplane radios energized and with a valid frequency selected befor connecting to SB4.End of the issue