Have been getting Internal Server Error for a while when saving posts, pages. Decided to deactivate all plugins as recommended. Jetpack would not deactivate ... generated the Internal Server Error. So I deleted via ftp. The errors related to saving posts and pages are now gone! Great! However, I now get that error when I go to the Updates page.
Tried reinstalling Jetpack, and I'm back to original situation with Internal Server Errors when saving pages and posts.
Have re-created .htaccess file and have plenty of memory for PHP ... two commonly recommended solutions.
Seems to be related to Jetpack since the situation is as described when Jetpack is the only plugin active.
thanks for ideas ...