If you are receiving an internal server error when attempting to create or liquidate a portfolio, then there is a few reasons why that may be happening.
The most common reason is the fact one of your API keys is invalid:
Let's say you are trying to liquidate your assets from three exchanges at the same time (we'll use GDAX, Binance, and Kucoin in this example). If Kucoin's and GDAX's API keys are invalid, then none of your assets will be liquidated and it will result in an internal server error. Same thing would happen when creating a portfolio as well. The only way to fix this is to disconnect your API keys, create new keys, and connect the exchanges once more.
You can determine which exchange is invalid by creating or liquidating an individual exchange portfolio. You will receive an internal error on that specific exchange indicating that is the one with the invalid API key.
Another reason might be your API's restrictions:
If your API keys only have read permissions on, then you will receive an error if you are attempting to enact a trade with that particular key. If that is the case, you will have to create new keys with both read and trade permissions enabled.
A similar case will happen if you try to transfer funds between exchanges with restricted withdrawals. To enable the transfer feature, you would need to have both exchange's APIs to be enabled for withdrawal.