Some people encounter a blank preview when generation an Invoice or Report on Mac OS X. This error can caused by Permission Issues with your Default Invoice Save Location folder. These permission issues can sometimes caused by an Operating System upgrade.
The preview could also show up blank if attempting to save your Invoices onto an external Hard Drive and the permissions aren't set correctly. Make sure the Default Invoice Save Location's permissions are set to read/write.
If you use Apple's File Vault, you may also run into issues with the Invoice Preview system in Studiometry.