Issue with V-lookup and possibly pasting data from the web?

Hi,

I'm hoping someone can help me. Using windows 2010, I'm using data from 500 alphanumeric codes that I copied-and-pasted from the net into a pre-existing Excel Spreadsheet.
Later, since these codes weren't put into the spreadsheet in a "V-look-up friendly" way, I started another sheet, and arranged them so they were all in the first column using the "=" in new sheet and referred to appropriate cell in the other sheet.
Then, with all of my other data lined up, I was able to create a third sheet where I extrapolated all my data and started using lookup.
Except, with about five percent of my data, Vlook-up is falsely returning a "N/A" result. I can go back to my original data, do a "Find" and I can see my data there. In the sheet I created, I can see the data in the sheet I created, but can't locate the data from "find."
What is creating this? I've gone as far as to copy and pasted the data manually into the appropriate cells, and even retying them in, hoping that maybe there was a "hidden character" in what I pasted from the net and that retyping it would somehow eliminate that. I created an "if then statement to see if the two data from my two sheets match each other, and Excel said they were. Still, vlookup doesn't seem to be recognizing the code, even though they are clearly the same.
Any help on this would be appreciated. For the time being I'm just manually ding a find and copying ad passing my data where I get the erroneous N/A's, but it bugs me when things don't work the wa they should, so I'd love a solution!

Thanks,
David