Steve, you have a calculated control somewhere that has a problem.
Once Access finds a control is is unable to calculate, it gives up trying to
calculate the others. Therefore one bad one can affect many/all the others
(depending on the order Access tries to calculate them.)
There are lots of things you could be looking for, such as:
a) You are attempting to operate on a field that is not on the report.
If you have a text box with Control Source:
=Sum([Quantity])
but there is no Quantity on the report, Access may optimise the report so
that the Quantity is not fetched. To fix this problem, add a (hidden) text
box for the Quantity field.
b) You placed a control in the wrong section.
For example, if you put:
=Sum([Quantity])
in the Page Footer, it will error.
c) There is a control that has the same name as a field, but it is bound to
something else. For eample, this will error:
Control Source =Sum([Quantity])
Name Quantity
d) You referred to a control in a subreport that has no data.
Fix:
http://allenbrowne.com/casu-18.html
There's lots of other reasons, but the basic trouble-shooting technique is
to make a copy of the report, and start dropping out calculated controls.
When the problem goes away, you have identified which one was the cause, so
work on that one. Repeat the process until all controls work.