Excel crashes with protected worksheet and hidden columns?

[Guest]

I have setup a worksheet with a number of cells containing formulas (concat,
vlookup, etc).

I have locked these cells and protected the worksheet (no password).

When I am in the last (unlocked) cell of a row and hit "tab", excel
completely freezes and i have to terminate it.

i would expect Excel to move me to the next row at the first 'unlocked' cell.

btw, the next column after the last 'unlocked' column is hidden. don't know
if that makes a difference.

Has anyone seen this before, and have any suggestions on resolution?

cheers.