To resolve this, you should try specifying the configuration file explicitly using the '--config' option when running your Walrus commands. Additionally, ensure the 'client.yaml' file exists at the specified path and includes the correct configuration settings. You might have to set it manually if it's not in one of the default locations such as ~/.sui/sui_config/.

The error 'Cannot open wallet config file' usually occurs when the command cannot find the wallet configuration it's supposed to use. A potentially common issue is having the 'wallet_config' field set to a string that is not a valid path, like '0xb...' instead of the path to a valid 'client.yaml' configuration file. Make sure to check and update the configuration parameter in your setup.

Downloading the latest configuration file directly from Walrus might also help. Use the following command to download it:

curl https://docs.wal.app/setup/client_config.yaml -o ~/.config/walrus/client_config.yaml

This will place the configuration in the expected default location, reducing the chances of a mismatch.