Excel 2007 : Bar chart x axis labels show up vertical!?

Greetings,

I have just created a workbook with one chart. I finished the project, saved the file, closed it and reopened it. When reopened the x axis labels for the chart (a column bar chart) changed from being aligned with the categories to all stacked under the first category (I'll try to attach jpg).

I have checked and played with all the settings I could find but to no avail. Any ideas?

TIA,
WD