In addition to setting the account that the Reminder service uses and giving the appropriate permissions, if you're running a SharePoint farm with multiple WFE servers there are extra steps required

The Reminder Web Parts send a message to the Reminder Service when the configuration has changed. The web parts use .NET Remoting over a TCP channel to send notifications from the Reminder Web Part to the Service.

By default the application configuration file is setup to only allow connections from the local machine and to use the first available port it finds.

If you are using certain types of Software firewall (NOT including Windows Firewall Service) on your Server then you may have to set SharePoint Reminder to use a fixed Port and setup your Firewall to allow this port to be used (Note - neither Windows Firewall Service or Hardware Firewalls should need any configuration for single web server installations as the communications do not travel across the network)

Also, if you are using a farm with multiple Web Front End (WFE) servers then you need to manually configure this part of the system and ensure that all the web-servers have a registry key set to enable the Reminder web parts to 'find' the server that the Reminder Service is running on.

1) Locate a free TCP port

Unless you have a preference for an unused port number then use using Port 1063 as this is very unlikely to be used by any other software. On the Configuration Tool select Server Settings and change the Remoting Settings to Manual and enter the Port number. Leave Reject Remote Requests unchecked as the web server the Reminder Service is running on will have to be able to accept requests from the other, remote, web servers.

After you have saved your changes you will have to restart the SharePoint Reminder Service.

2) Copy the registry key

The registry key at HKEY_LOCAL_MACHINE\SOFTWARE\Pentalogic\SharePointReminder\1\IpcURL will have the information entered into the Configuration Tool and this registry key will need to be copied onto the other web servers in your farm.

The easiest way to do this is to use RegEdit's Export command to export the key in a .reg file and then run this on the other web-servers in the farm.

Before you install the .reg file on the other WFE server you must open the .reg file in notepad and ensure that the IP Address listed is the non load ballanced IP address of the WFE and not 127.0.0.1 - edit if necessary