Yes, we are doing silent installs (with a few parameters if that matters). However in the script we set SILENT=FALSE and show only progress dialogs without a cancel button.
I forced the setup to unpack to a removable media with no free space, in both silence and non-silence ways, and both of the times I get a return code of 1.
Please, try to run the same setup but in non-silence mode, as you will get a message box with a description of the error, and post it here. Thank you.