You should understand the difference between a pruned wallet, pruned blockchain and a normal wallet. In a version of Bitcoin Core which runs pruned blockchain (which you use now), i.e a part of older blocks are deleted and the total size of the chain is reduced to match the stability of your computer. When the blocks become old, they are eventually deleted while you are running a pruned mode. So, whenever you import a wallet or addresses to Bitcoin Core, the
-rescan rpc option is triggered by default. This will rescan the whole blockchain and will update your currently imported wallet balances.
Since the pruned mode doesn't have the whole blockchain, the rescan option has been disabled in pruned mode and since the Bitcoin Core cannot run
-rescan option, the importing of wallet option is disabled in pruned mode. I guess, the default option for triggering the rescan should be false while importing wallets and addresses but this doesn't help you really.
Apart from being a full node, Bitcoin Core is a wallet as well. Rescan option is important for you to know about the current balances of the wallet and to prevent further double spending or transaction problems. So a newly imported addresses and wallet requires to run rescan option which can never be done with a pruned node.
See this code from
bitcoin/src/wallet/rpcdump.cpp to know about this issue
if (pwallet->chain().havePruned()) {
// Exit early and print an error.
// If a block is pruned after this check, we will import the key(s),
// but fail the rescan with a generic error.
throw JSONRPCError(RPC_WALLET_ERROR, "Importing wallets is disabled when blocks are pruned");
}
Don't forget to use the -rescan you can do this by going to Program Files>Bitcoin and open command prompt under that folder by holding shift key then right-click as shown as in this image below.
OP is running the wallet in pruned mode,I guess
-rescan would never work as per the code.
P.S @Engelen what I have said is the basis for your error, if you would like to import the wallet follow @jackg's first post in this topic.