Afaik for Application Roles to take place, user should re-login -- Roles are assigned on login. So -- no need to restart the web application, but user should log out and login again.

And yes, Application Roles is a great tool to minimize privileges that are given to the user directly

a) Try setting error page as %CSP.Error.cls for this web application, then errors are shown on the page itself, instead of being logged

b) Reproduce the error with ^%ISCLOG enabled:

kill ^%ISCLOG
set ^%ISCLOG = 3

Reproduce the error quickly.
Disable ^%ISCLOG

set ^%ISCLOG = 0

Check for errors in ^%ISCLOG:

 zwrite ^%ISCLOG

Also, you can create calculated dimension member and sort members by PROPERTIES("KEY") using following expression:

ORDER([DateOfSale].[Actual].[DaySold].Members,[DateOfSale].CurrentMember.PROPERTIES("KEY"),BDESC)