I don't think it is related to the General format since that only
impacts the display properties of the cell. It sounds to me like the
second set of data may have been imported from another application. I
often ran into this when copying the results of an Access query into
Excel. Excel would think the numbers were really characters. There
are a couple of fixes available. I don't recall the exact fix so you
give them a try.

Perform a Copy - Paste Special/Values. (I assume you know how. The
quick version is highlight the column, pick Edit | Copy then Edit |
Paste Special | Values and press OK. Then escape to unselect the
column.

Multiple all values by 1. In a separate column, enter a column of 1s.
Highlight the first column, pick Edit | Copy, then select the column
with 1s and pick Edit | Paste Special | Multiply and press OK. Delete
the first column.

Hope that helps.

- John