In order to resolve this you need to enable 'Holiday' permission in your Administrator permission.
Please follow the steps below:-
1. Log into Replicon as Administrator. 2. Go to Administration > Users. 3. Edit your account > Go to Roles & Permissions. 4. Make a note of the permission assigned for Administrator. 5. Go to Administration > Permissions Sets > Edit the Administrator permission. 6. Under Permissions for System Data > Enable View & Edit for Holidays.