Hi. This is in fact a memory issue as the error states. While you have loaded extra records in the database, those records return to wordpress as wordpress queries for results and attempts to hold them in memory during the process you're attempting to do when you see the error.
There are a couple of steps which can be taken to fix this, and I'd be happy to try them for you. I'll do this prior to you awarding me the project... and once it is solved/fixed and you're satisfied then you can award and pay.
I'll need access to FTP, or if not, to your host account so I can access the file manager. Actually what host are you using? Your hosting package may be playing a part in this memory error.
If you can take a look at my profile/feedback you'll notice I'm a 100% trusted freelancer with an excellent reputation and great communication. Total 10+ years in the IT Industry with a few years of stuff like wordpress and webhosting under my belt, in addition to two Microsoft Professional Certs.
I'm from the Caribbean, english speaker, and our time zones should be close as well. Looking forward to hearing back from you. Regards, Kenny.