Web2py scheduler stopping the app from running

Question

I cann't get the scheduler run in my ubuntu or debian linux machines. Originally I had db = DAL('sqlite://storage.sqlite') which causes a weird situation where the website becomes unavailable (the browser cannot establish a connection to the server at 127.0.0.1) but when I run the same app without scheduler (without -K appname), and check the app database, it shows that the scheduler task has been running successfully. What is causing connection to the server to break? Second, I tried using pymysql or mysqldb instead of sqlite. but, I get this error "Error in URI 'pymysql' or database not supported" even without -K myapp option.