Right Grahame Jordan but you want to force fully stop then you need following step.

• Stop OpenERP Server
• login to postgresql database (with selected database)
• fire following query
  "select * from ir_crom;"
• check what you try to edit or create perticular form is it under in ir_crom if yes then get that id and fire following query
• """update ir_cron set active = False where id = (Selected id);"""
  (inactive all scheduler)
• Start openerp server and login and do your work.

While the cron is running a job it will block writes to the ir_cron table. You need to wait for the job to complete. If you are running the mrp scheduler this may take a while

Problem due to most continue working scheduler and access all most resources.

I had read a article where problem fixed somehow, Its work for me.

Steps to fix

http://goo.gl/vZSYd1

I suggest to OpenERP Bugs fixer to resolve this issue with OpenERP 7.0 first.