How to Sequence the Silent Installer .exe file before installation of main application in Custom Action Sequence?

I am trying to Install a custom exe file before I Install main windows installer file.

I am using Install Sheild Limited Edition. After configuring everything I have sequenced my silent installer file at "After Register Product stage" of Custom Action and it gives me error 1618(which is another installation is in progress.) I got that the main installer is in progress so it is not allowing silent installer .msi to install, but don't know how to resolve this error.

But the issue is I am Selecting Source Location as "File Exist on Target Computer" and File Location as "INSTALLDIR".

Upon doing this I am getting an error 1618.

Can Anyone help me to resolve this?

The Code inside SilentInstaller.exe file is as below:

Process processObj = Process.Start("msiexec.exe", @"/i "folderpath\SqlLocalDB.msi" /qn IACCEPTSQLLOCALDBLICENSETERMS=YES");
                            //Loop until the process has exited
                            do
                            {
                                //refresh the process
                                processObj.Refresh();
                            } while (!processObj.WaitForExit(1000));

I have verified the path and everything but got struck in the sequence only.

Any Help will be much appreciated. Thanks.