Error message upon login

I got InvoicePlane installed and working, but now when I login, I get this error:
An Error Was Encountered Unable to load the requested class: crypt

Strangely, no errors for InvoicePlane show in the PHP error logs.

Please make sure that your web server meets the requirements
It seems mcrypt is missing.

@Kovah It was working fine for a while and then did this all of a sudden after I had made several invoices. There were no errors on the install page where it checked everything.

@Kovah, I reinstalled and it works again. But this is the 2nd time I’ve had to reinstall in the 3 days I’ve been testing. Hopefully this doesn’t happen again. It has been happening at random times for no apparent reason.