Just to add to what Technical Support posted:

There has been a recent update to Invoices. The current release is (031223). This update contains new sample data that would allow you to check whether your problem is data related (although Tech Support is probably right about the newer Crystal print engine).

You should change the opportunistic locking settings ASAP.

Have you recently changed anything else about your computing environment? New Server? New workstation? New workstation OS?