Identify which dll failed to register. During the installation, a message box will popup alerting you and detailing the error and offending file is shown. However, to be safe, you may want to generate an MSI log for support to analyze in the event that other errors have occurred in the installation.
Usually, this error is caused by inadequate registry permissions on the installation machine. Though you have administrative rights, for some reason registry branches that our installation needs to modify have been altered to exclude certain groups or users. Because of this, when we attempt to register certain dlls, regsvr32 fails and you see the 1904 error. It is uncertain as to why permissions are being altered though it must be noted that our inability to install is a symptom of the problem not the cause; software from other vendors may exhibit similar behavior.
Finish the Installation. Depending on the state of the install, merely registering the dll may have made the product fully functional. Unfortunately, this is not always the case and they may have to choose a 'Repair' install from Add/Remove programs or even fully reinstall the product.