404 permalinks after page edit

When editing a page all my permalinks redirects to 404 page..

i’ve read lots of articles saying switch back to default permalink(?p=123) save it and then edit again using custom permalinks to regenerate the .htaccess file..

Now,all the permalinks are working but the problem is every time i edit a page or add a new page, all my pages redirects to 404..

before the development, i imported the post and pages from xyz.com to xyz.com/dev

help… really need your help on this..