By Graham K. Rogers

Earlier today, I had the unusual experience of a red flag from the Mac App Store when an update for Autodesk 123 indicated that the "Preflight file" had not been signed by Apple so could not be downloaded. I tried a fix that was suggested online with the preferences to Keychain Access, but that was not succesful.

While washing the coffee pot (one of those free moments, like shaving or shampooing my hair that let me think), I analysed the problem. Difficulties may be external or internal. The external would include Apple's own certification and the app, as well.

Internal could include preferences for OS X (the last reboot was 11 days ago) and network differences as I switch from home to the office. I had experienced problems when using the proxy server at the office in the past, including synchronising with iCloud, so wondered if that may be part of the problem.

The last time I had updated an app (Polarr - 9 February) it was plain-sailing. An obvious place to start would have been a restart of the Mac to see if that would make a difference.

When I arrived at the office, I looked at the App Store again to see if the Autodesk 123 download would report the same, but there it was gone. The app itself, shown in Applications as 123D Design, opens and works fine.

As a double check (triple-check actually), I tried different networks: the university, iPhone Hotspot and another non-university connection I sometimes access. Each time I clicked on the update button in the App Store, it showed that nothing was available. I now presume (fingers crossed) that the problem relates to the certificate at the App Store end and this will be fixed sooner or later.

Curiouser and curiouser. . . .

Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand. He wrote in the Bangkok Post, Database supplement on IT subjects. For the last seven years of Database he wrote a column on Apple and Macs. He is now continuing that in the Bangkok Post supplement, Life.