I have found a bug in Tronlink Mathwallet Tronwallet that will not let you load long privkey privatekey despite its a good one. This problem will mostly harm initial TRX Tron investors of Justin Sun, as they have old backups that will not work.
Tron Wallet Backup has different code.
If you use current TronLink or other wallets you use seed key (mnemonic words) or privkey (64 characters). But back then when Tron TRX came to live from Ethereum ICO, the priv key was of 128 characters. Right now there is no wallet that can import this and your coins are lost. 128 bit private keys dont work, and initial legacy holders of Tron are left with nothing.
Solution to this Tron not accepting long private key backup wallet
You can use older versions of Tronlink chrome extension, but it will only let you import the keys. You will not connect to the nodes of Tron TRX as it uses different types of nodes – solidity, 8090 ports and 8091 ports on API RPC TRON.
After over 24h of work we have found a way to send out TRX Tron to new wallet despite old private key, but for this i have to be contacted privately. For now Tron Foundation nor Tronlink team has no easy solution and our takes a lot of work but we managed to take all coins out from glitched private key wallets of Tron.