Error bars not displaying properly

Hi,

I have plotted my data in a column graph, and added error bars based on
custom values. I know how to edit and format the error bars, but nothing I
have changed fixes my problem:

The error bars "join up" to give diagonal lines between between my columns.

I have NEVER had this issue in previous versions of Excel. If I plot the
error bars in pre-2007 excel, they're fine, until I open them in excel-2007.
If I remove the error bars, and plot them afresh in excel-2007, I get the
same problem.

It doesn't happen to every error bar, just some of them, for no apparent
reason.

How can I stop them doing this?