[ERROR ITMS-6000: "Unknown or unsupported package version [software5.10]."]

I'm running into the same issues with the Xcode 10 straight from the App Store (was also happening with the GM). My XML seems correct so I'm not sure why it would be complaining about the root version? I'm thinking iTMSTransporter might not be set to the proper version.

@catloafsoft: Thanks for your reply, at least I'm not the only one facing this problem. Since you mentioned that the official new XCode version is available, I thought I should give it a spin as well. It does come bundled with Application Loader 3.7.2 and iTMSTransporter 1.12.0, but the error is the same for me (Also software5.10).

Anyone got an idea how to solve this problem?

Yep:
1) About 2 days ago "iTMSTransporter -m lookupMetadata" started returning a metadata.xml with:
<package xmlns="http://apple.com/itunes/importer" version="software5.10">
2) But "iTMSTransporter -m verify" with the same package version errors. The XML schema does not appear to be different from "5.9", so setting back to that works, i.e.:
<package xmlns="http://apple.com/itunes/importer" version="software5.9">

Two days ago the App Metadata Spec implied 5.10 was release "September 19, 2018 - Version 5.10" (?!):
https://help.apple.com/itc/appsspec/#/itcfdbb559d7
.... seems like something's out of sync at appstoreconnect, maybe it'll correct by end of today?

@Zuikyo @nanashi: Thanks a lot, changing back to version 5.9 works for me. So probably version 5.10 will be available within the next days, so we can upload images for the iPhone XS Max, right?

Thanks a lot for the help!