Hi userkcwlui,
Getting error messages while doing your work can be time-consuming. QuickBooks is a versatile program that offers a variety of features which make your work easier. I'd be glad to give you a hand so you can focus on what's important to you.
Based on the error you've described above, it's vital to make sure the currency you're using is correct. Usually, that error happens when you're trying to process a transaction which doesn't match your home-currency. Once you've verified that the currency you're using is correct, I recommend processing the advance petty cash to your employee again.
If you run into the same error again and the currency is correct, I recommend clearing cache and cookies as this usually fixes most browser issues. You can do this by following the steps in this article: Clear Cache and Cookies. I also suggest trying a private/incognito window and let me know what happens. Give this a try and remember that I'll be one message away if you need anything else.