why i an blunder after shutting windows forms application?

when i run visible studio windows forms concentration clicking f5 (debug mode), after i click tie symbol (which calls application.exit()), after few seconds
i an blunder says:

cannot acess likely object: vigilant name 'sampleform'.

a bit background, i have another thread runs each x seconds.

my speculation i tie application, given still debug mode, thread still controlling tries opening something
but given i tie concentration form disposed.

is correct?

do i have kill credentials slight thread before i application.exit()?

update

now i thread.abort() before application.exit() concentration closes completely. before, even after i clicked tie button, debugger still controlling (i.e. stop symbol selected) contingency have since thread still active).