Hi guys! It's been a while since I posted something I encountered or stumbled upon that can help anyone... so here it goes.
I recently got a stint to migrate a client of mine to Google Apps for Work. Their old email set-up was relatively simple, and they asked me to migrate their old email data that was stored in their desktop-installed Outlook 2013 client. Although they're using a 64-bit Windows 7, I'm not quite sure if it was also a 64bit Office 2013 that was installed as they're the ones who did it. Once I exported their data with the "export to file/PST" function of Outlook 2013, I was about to make my move.
What I initially did...
I used one of their workstations (that already has Outlook 2013) and installed GAMME (ver. 5.0.25 to this writing) to be my migration staging area. I then followed and executed the necessary pre-requisites (API and json token permission and service certs). Once I was ready and prepared the userlist file and PST folder structure, I proceeded to start-estimate-migrate using the GAMME tool.
Everything went well initially and passed the testing and estimation. Once I reached the migration part, all the user accounts failed to migrate, with an "Error 80040154" kept showing up for each user.
Initially I thought it was the network but I was easily able to rule that out after some cable management and connected directly to our broadband modem/internet. I also checked if the Outlook 2013 was up-to-date, which apparently it was. I tried and looked for quite a long time across various support materials, forums and How-To manuals of Google for the GAMME tool but to no luck or even a mention of that particular error code.
It led me to conclude that the culprit might be the Outlook 2013 itself as I already had experience in the past that the migration tools Google provides only behaves correctly on legacy (or not a recent release) Microsoft products. Despite the GAMME website saying it supports Outlook 2013, it's not the first time I didn't believe in Google as they have a reputation on not properly maintaining any support/admin tools nor keeping their documentations up-to-date.
I used a different workstation without the Outlook 2013 installation and then installed an Outlook 2007 (32bit) and downloaded the Office 2007 SP3 standalone patch since the GAMME tools requires Outlook 2007 SP2 at minimum. Once that's done, I installed again the GAMME tool and made the necessary set-up requirements... then it now works.
Hope I'm able to help anyone out there who might face (or currently in) this same dilemma. Cheers!