For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
i upgraded to latest as u said , now it doesnt submit the form , but it doesnt pop up the calendar to select dates ??You should use the latest code from GitHub (joomla3 branch).
Did you clear Joomla and browser cache?
Are you using a standard Joomla Bootstrap template (compatible with protostar)?
Fabrik bootstrap form template?
Which browser?