I have my original dat file from an old version of the desktop swing wallet, which just stopped loading and showed error messages. I have downloaded Desktop GUI wallet 0.75.8 currently, how do I use my old dat file to retrieve my token balance into this new wallet? Thank you for any help!!
If the wallet has stopped loading you most probably have the known “broken local blockchain” problem. You need to reindex the blockchain. Reindexing of the broken block-chain may be necessary even if you use the new/latest version of the wallet. For details of how to reindex, see the troubleshooting guide: https://github.com/ZencashOfficial/zencash-swing-wallet-ui/blob/master/docs/TroubleshootingGuide.md
The following step-by-step guide for Windows users (created by a third party) is also handy: https://miningwithnvidia.com/2018/02/09/zencash-wallet-eof-reached-code-1/18 to help with reindexing in case of encountering the common block-chain problem.
Generally regarding backups: The ZEN private keys are located in the wallet.dat file in directory:
Mac OS: ~/Library/Application Support/Zen/
To make sure your ZEN is not lost, the most important thing is to keep a backup copy of your wallet.dat file - it must never be lost! It may be copied manually when the GUI wallet/zend are not running. The wallet.dat needs to be backed up regularly (not just once - say after every 30-40 outgoing transactions) and it MUST also be backed up after creating a new Z address.