I have had similar problems with Excel, I found it was converting a text field to number when saving on a different machine. Excel was showing a cell as number even if it was formatted as text, hence your decimal places.
Try opening your Excel file and in a seperate column use the formula =Text('The number cell',0). This will take your number cell and convert it to text. Then copy this cell over the original number cell and paste as values. Repeat this for all cells in the offending column.
Hopefully then the Monarch Lookup should find a text field it is looking for and work OK.
Hi, and welcome to the forum.
I just want to offer another option to Nigel's great option of converting numbers to text that I have used is to hi-lite the entire column or just the range numbers and then on the toolbar, select "DATA", under that, select "Text to Columns". This opens the "Text to Columns Wizard". In the first step select "fixed width", then hit next twice to get to step 3. There, under "Column data format", select "Text" and then press "Finish".
This is quick and easy method and if you want, it is easy to write a macro or script to automate this.
Try both methods and decide which works best for you.
I finally had a chance to try the suggestions. Nigel, I couldn't get yours to work. however, I only tried once before moving on to the next option and it worked. Thank you both so much for your help! Now I know where to come if I have any more problems rather than wasting so much time trying to figure it out myself.