Cannot create invoices or customers

Hi,

Since yesterday I receive an internal server error when I try to create new invoices or customers. I can create bills. My only idea is that it's related to the custom fields, we have custom fields set up for customers and invoices but I cannot even access the custom field setup any more to remove them. Is this because of the update?

I uninstalled custom fields and it works now... Will it stop working again if I reinstall it?
Anyway I see that if we upgrade to the standard plan, we will loose the custom fields as it is not included. But it's paid until march next year, what happens in this case?