Importing wallets is disabled when blocks are pruned (code -4)


I tried to upgrade my wallet from Blockmarket 1.??.
My old laptop died but i still have a backup of the directory:
/Users/USERNAME/Library/Application Support/Syscoin
which includes the wallet.dat file.
I followed this guide:

To do the dumpwallet i had to install Blockmarket 1.2.3 where i simply changed the Syscoin folder with my backup folder. After that i could see my coins in the wallet.
After that I installed Syscoin 4.3.0.
But the last step of the guide is not working for me. When i try to Import my sys3dump.bmwalletdump file, the console gives me the error:
“Importing wallets is disabled when blocks are pruned (code -4)”.
I tried the import on an other PC with a new Syscoin 4.3.0 installation. Same result.

Is there a Problem with my dumped wallet?
Or does an other way exist to get my privatkey out of my wallet.dat file?

Thanks for your help.