Custom Update runs locally on clients computers. So when the client read :
You need to add the file as an additionnal file. And, in the custom update wizard, just put the name of the file.
Take a look to this how-to : https://www.codeplex.com/Download?ProjectName=WsusPackagePublisher&DownloadId=691788
<PathToExecutable>C:\WSUS Package Publisher\Updates\One Package does all JAVA 32bit\jre-7u60-windows-i586</PathToExecutable>The client try to find this file on the local hard drive . Do you really think this file is present on the hard drive of the client ? I don't think so.
You need to add the file as an additionnal file. And, in the custom update wizard, just put the name of the file.
Take a look to this how-to : https://www.codeplex.com/Download?ProjectName=WsusPackagePublisher&DownloadId=691788