Try this. 
https://www.ibm.com/support/pages/filenet-enterprise-manager-throws-error-when-connecting-content-engine-over-tls-12

Else please create a case for support assistance. 

Add the below registry key and see if it works. 

This worked for me,

Edit the rrprocessor.exe.config (C:\Datacap\Taskmaster)

Add the below line to the rrprocessor.exe.config file:

<AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>

The modification should be performed as follows (new line is shown below in BOLD):

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

 <runtime>

   <AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>

   <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">

      <dependentAssembly>

         <assemblyIdentity name="System.Net.Http.Primitives" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />

         <bindingRedirect oldVersion="0.0.0.0-4.2.29.0" newVersion="4.2.29.0" />

      </dependentAssembly>

   </assemblyBinding>

   <generatePublisherEvidence enabled="false"></generatePublisherEvidence>

   <loadFromRemoteSources enabled="true"></loadFromRemoteSources>

 </runtime>

</configuration>

Hope it helps,

Bob

Add the below registry key and see if it works. 

Good finding Bob but probably best to stick with the technote or as Varum did to solve the issue. 

This worked for me,

Edit the rrprocessor.exe.config (C:\Datacap\Taskmaster)

Add the below line to the rrprocessor.exe.config file:

<AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>

The modification should be performed as follows (new line is shown below in BOLD):

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

 <runtime>

   <AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>

   <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">

      <dependentAssembly>

         <assemblyIdentity name="System.Net.Http.Primitives" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />

         <bindingRedirect oldVersion="0.0.0.0-4.2.29.0" newVersion="4.2.29.0" />

      </dependentAssembly>

   </assemblyBinding>

   <generatePublisherEvidence enabled="false"></generatePublisherEvidence>

   <loadFromRemoteSources enabled="true"></loadFromRemoteSources>

 </runtime>

</configuration>

Hope it helps,

Bob

Add the below registry key and see if it works. 

Extending this topics - Does anyone know what ciphers is being used for RuleRunner. 
Thinking this through the logic - The RR server communicated direct to the TM Server via tcp ip.  TM server is enabled for  TLS 1.2 and the Database accepting TLS 1.2.  These Cipher option are like TLS granular sub cipher encryption type which one does it use?  

Good finding Bob but probably best to stick with the technote or as Varum did to solve the issue. 

This worked for me,

Edit the rrprocessor.exe.config (C:\Datacap\Taskmaster)

Add the below line to the rrprocessor.exe.config file:

<AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>

The modification should be performed as follows (new line is shown below in BOLD):

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

 <runtime>

   <AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>

   <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">

      <dependentAssembly>

         <assemblyIdentity name="System.Net.Http.Primitives" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />

         <bindingRedirect oldVersion="0.0.0.0-4.2.29.0" newVersion="4.2.29.0" />

      </dependentAssembly>

   </assemblyBinding>

   <generatePublisherEvidence enabled="false"></generatePublisherEvidence>

   <loadFromRemoteSources enabled="true"></loadFromRemoteSources>

 </runtime>

</configuration>

Hope it helps,

Bob

Add the below registry key and see if it works.