Numbering won't continue

[Sloth]

I am numbering my sections using the "Numbering" button on my toolbar. When
I right click the number and click "Bullets and Numbering" the "Continue
previous list" is greyed out. I don't have any section breaks or anything
like that. It looks something like this...

1. Section 1
normal text here
1. Section 2
normal text here

The "1" next to Section 2 should be a "2", but the option "Continue previous
list" is greyed out. What causes this?

I am using Word 2000