User manager v3.0 not able to “disable or delete” a user.
Can you please help? Is it a bug? I`ve been having this problem since I upgraded to userman v3.0? 
try opening it on mozilla firefox browser.. seems like userman page has issues with some versions of Internet explorer
Make sure that you have the latest version of the RouterOS (where User-Manager is installed).
If you will have problems with the latest User-Manager and IE, please contact support about the issue (support@mikrotik.com).
Report back with the results.