Pokemon Leaf Green Save File Problem

[MalusCalibur]

I was hoping someone could help with some strange behaviour a Leaf Green ROM save file is exhibiting. The game was being played on a DS Lite using an M3DS Real flashcart, a device I have played GBA games on (including Pokemon ones) for quite a number of years. At first it was working fine, saving and resuming as normal over the course of a couple of days. However, seemingly at random it showed the message 'The save game has been deleted...' when attempting to start it up today. I investigated this by trying to play the save file on VBA-M on my desktop, but the same issue persisted. However, opening the .sav file with PokeHex reveals that all the save data is still present there; all the Pokemon in the party and boxes are as they should be, as are all the event flags etc. It would just appear that the emulators in question are playing silly buggers and are not able to correctly load it. I attempted to change the ROM directory in VBA's settings, but this did not work.
The .sav file is 128kb, which is the correct size, and as mentioned the save/load function has been working fine until now - it seems to have just arbitrarily stopped doing so.
What steps can I take to recover it? Presumably this must be possible if the data is there and recognised; and the person playing really does not want to lose their progress. I have enclosed a copy of the .sav file for inspection if necessary.
Any help you can provide will be appreciated.

 

[metroid maniac]

Are you using the M3 GBA Expansion Pack to play this game?
Maybe the battery in the cartridge has run out.

 

[MalusCalibur]

Are you using the M3 GBA Expansion Pack to play this game?
Maybe the battery in the cartridge has run out.

I am - though it's possible that's the cause, it seems odd that the VBA-M emulator has the same issue as that is entirely divorced from the expansion cartridge.

 

[Deleted member 661761]

There were some wrong checksums that i fixed with pkhex and now, at least on vba-m, it works

 

[MalusCalibur]

There were some wrong checksums that i fixed with pkhex and now, at least on vba-m, it works

That does seem to have done the trick, thank you!
Can you identify what might have caused those checksum errors, and how to spot them, so I can perhaps prevent this from happening again? To my knowledge the player didn't do anything unusual, such as powering off during a save.