Pilot2atc changes squawk code prior to takeoff

[aparso16 0]

I have had this several times now that I am given a squawk code  by clearance and all is fine until I get to the runway where by atc then advises to change squawk code to 7000. Why is this . Am I doing something rong?

 

[Dave-Pilot2ATC 870]

You're making a change to the flight plan or doing something that causes the program to think you are taking off VFR instead of on the IFR flight plan you filed.  Once you file a plan, don't make any changes to it or disconnect from the SIM.  If you do, everything can reset so you must start over with the filing and obtaining clearance.

Dave