Hi I have a Problem with my AirPort Express 2005

Yes. Version 6 of Airport Utility was released in 2013 when OS X 10.8 Mountain Lion was the current version. I'd imagine you'd need 10.8 or earlier (but no earlier than 10.4 Tiger) to support Airport Utility 5.4.2

Your Express is obsolete and requires Airport Utility 5.4.2 for configuration. This was retired long ago and won't run on recent versions of macOS.

You cannot configure that version of the Express with the version of Airport Utility which replaced 5.4.2 - the last of which was 6.3.9 and which continues to be supported by recent and current versions of macOS.

This is ancient history. I found version 5.6.1 (2012) for Leopard (10.5) and Snow Leopard (10.6) although I can't tell if it's an updater to version 5 or an installer. It's the latest I could find.

My old 10.13 Mac does not support this version either, so you'd have to go back to Snow Leopard I would conclude. It's on the Mac - because I never bothered to delete it - but only version 6 will launch in 10.13 High Sierra.

Hi,

Also, if necessary, and if you have or could borrow an appropriate Windows PC, you may want to try one of the pre-5.6.1 AirPort Utility for Windows versions available via Apple - Support - Downloads Peripherals (repeatedly click the Load more results button until the older downloads are shown).

AirPort Express - Technical Specifications

Apple – Support – Downloads (DE)

Are you possibly referring to a text in an old article HT5022 (How to set up and configure an 802.11g AirPort Extreme Base Station or AirPort Express in OS X Lion)?

"If you are using OS X Lion and wish to set up or configure an older 802.11g AirPort Extreme Base Station, or 802.11g AirPort Express, manually download and install AirPort Utility 5.6. AirPort Utility 5.6 can be used to configure earlier 802.11g AirPort Extreme Base Station, and AirPort Express; it can also be used for 802.11n AirPort base stations."

This does not necessarily rule out some earlier AirPort Utility versions. My information was about pre-5.6.1 versions for Windows.

I seem to recall that it might have run on later systems. I have a 10.13 installation on an older Mac and I'll see if it also had Airport Utility 5 on it.