Hey! I see it's been a few years, not sure if you ever ended up resolving this issue, but I found this thread because I am dealing with a similar, albeit less severe, issue. I also have a Pokemon Emerald cartridge that I purchased from Walmart myself back in like 2005 or something, so I know the cart is authentic. I picked it up last year to play through it again and started having troubles with it. Sometimes when booting the game, it does not leave the GBA title screen. Other times, it does but then the screen just goes white after. Sometimes the game appears to be working fine but then when I try to save, the game will freeze during saving (which ends up corrupting the save file). I got decently far into the game last summer and this happen to me where I lost the save data on the cartridge. I managed to get it working again and started another file which I was able to play through to completion. Last night, my Emerald cart started acting up again. I was trying to trade between my FireRed version and 3 pokemon in, the Emerald version froze while saving after the trade. It sat there for a while it wasn't saving, and then the screen just went completely black (sound was still on). After a few seconds, it brought me to the screen you posted up above saying "Save completed, game can no longer be played, returning to title screen." It did and somehow retained the save file on the Emerald, tho it also corrupted the save data on my FireRed game (also retained previous save). Thankfully, I had just backed up both games' saves on my GB Operator because when I rebooted the Emerald, I was stuck in this weird glitched trade room that I was unable to leave, so the game was essentially soft-locked.
I thought I got it working again and played for another several hours saving multiple times and backing up the saves. However, when I booted it up this morning, those several hours were not present on the file and even the saves I backed up were corrupted and not working, so I was unable to restore the data. Something is seriously wrong with this Emerald cartridge and it's saving. I originally thought cleaning the pins would help, but it didn't really. My Emerald is still able to retain a save, but sometimes it just stops booting/ working properly and will start freezing, which eventually leads to corrupted save data (because it just won't save and then I have to turn the power off during the infinite save).
After doing some searching online, I was able to deduce that this may be a problem with the solder joints on the Flash memory chip. The PCB is quite thin and it seems the repetitive motion of inserting/ removing the cart from the GBA can cause stress and potentially fatigue the joints over time. I think it's much more likely this is what's happened to your Emerald, than the chip itself going. I've seen several videos of people fixing GB/A games that won't boot/ save properly by simply reflowing the solder joints on the mask ROM and RAM. I'll attach some links.
Anyway, I thought I'd post this here in case anyone else is having this problem, or if you yourself have figured it out! What's interesting is that although I did play my Emerald growing up, I didn't play it nearly as much as my Ruby and FireRed version. Yet, my Emerald is the cartridge with problems and when I was researching, it seems many others have similar issues with specifically Pokemon Emerald and saving. I wonder if Emerald potentially had a factory defect that is interfering with the RAM. I haven't actually attempted to repair my Emerald yet because although I have an idea of what may be the problem, I do not have a soldering iron/ station, nor any experience soldering and the pins on the GBA carts are extremely small. I'll have to come back and update when I eventually get the confidence to attempt this, or find someone who can service GBA carts. Cheers.