Q&A Problem - 404 error

I've installed Q&A (v1.0.3 BETA 3) for my site (v3.2.1).
Yesterday...I noticed that all Q&A page is "404 Page not found".
So, I read this page; https://premium.wpmudev.org/forums/topic/just-getting-4040-errors.
The result is....

Settings > Permalinks custom -> /%category%/%postname%/
mysite/question -> 404 Page not found.
mysite/question/ask/ -> 404 Page not found.
all archives -> 404 Page not found.

[[[ installed the debugging scrip ]]]
#0 log_rewrite_flush(rewrite_rules)
#1 call_user_func_array(log_rewrite_flush, Array ([0] => rewrite_rules)) called at [/wp-includes/plugin.php:405]
#2 do_action(delete_option, rewrite_rules) called at [/wp-includes/functions.php:667]
#3 delete_option(rewrite_rules) called at [/wp-includes/rewrite.php:1877]
#4 WP_Rewrite->flush_rules() called at [/wp-content/plugins/my-calendar/my-calendar-core.php:13]
#5 my_calendar_add_feed()
#6 call_user_func_array(my_calendar_add_feed, Array ([0] => )) called at [/wp-includes/plugin.php:405]
#7 do_action(init) called at [/wp-settings.php:302]
#8 require_once(/wp-settings.php) called at [/wp-config.php:96]
#9 require_once(/wp-config.php) called at [/wp-load.php:29]
#10 require_once(/wp-load.php) called at [/wp-admin/admin.php:30]
#11 require_once(/wp-admin/admin.php) called at [/wp-admin/options-permalink.php:10]
-------------------------
Deactivate my_calendar plugins. -> 404 Page not found.( all pages )
-------------------------
Settings > Permalinks default
mysite/question -> 404 Page not found.
mysite/question/ask/ -> 404 Page not found.
mysite/?post_type=question/ -> OK
all archives -> OK

[[[ installed the debugging scrip ]]]
#0 log_rewrite_flush(rewrite_rules)
#1 call_user_func_array(log_rewrite_flush, Array ([0] => rewrite_rules)) called at [/wp-includes/plugin.php:405]
#2 do_action(delete_option, rewrite_rules) called at [/wp-includes/functions.php:667]
#3 delete_option(rewrite_rules) called at [/wp-includes/rewrite.php:1877]
#4 WP_Rewrite->flush_rules() called at [/wp-admin/options-permalink.php:125]

Please help me!