The green triangles don't actually say there's an error, just what Excel thinks is an inconsistency.

To convert a 'numerical text' range to numbers:
• input a 1 in an empty cell
• cut the number
• select the range to be modified
• choose Paste > Paste Special > Values > Multiply > OK
Note: you can select a whole column for this, but any empty cells will end up with 0s in them and any cells containing formulae will be converted to their results (ie the formulae will be lost). Text will be unaffected.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]