newPerformScriptCommand Question

I have a php page using the FileMaker PHP API that performs a FileMaker script using the newPerformScriptCommand method - this all works well so far. The script performs a bulk email to a selected group of records and can include an attachment.

We've found an issue where if someone selects a reasonably large attachment (e.g. a 2mb PDF) the FileMaker script will still send the messages successfully, however the php script encounters an issue and i get "The page cannot be displayed because an internal server error has occurred." in the browser and there's a 500 error in the IIS log file for the script.

Does the php script have to wait for the FileMaker script called by the newPerformScriptCommand to finish running before it can continue? We don't need to wait in this instance for the FileMaker script to finish as we would like to continue and let them be sent on the server. Has anyone else encountered this issue with a long running FileMaker script?

thanks,

Steve