Hi Arthur,
Do you see your columns show up in the control list (the lower right-hand panel in #2 reply fro Chris?
If so, they are actually created - but - they are located way out to the right in design mode. Every now and then some DB driver will tell PB's DB interface that an expression or a column is way wider than expected. When THAT happens you get a layout that appears almost without content - but scrolling to the right - or click on each control in the control list - will display each column, even the computed.
Sometimes, the issue is that column has width = 0 (hiding in plain sight). Again, the actual control to display the column will be part of the control list.
HTH /Michael