Data Placeholder cannot be found

Not sure if this info helps to explain... But I was able to import my data source into Indesign without any issues, until I hit preview in the data merge window so that I can see all the information being pulled, live.  

This is when I get this error. So from this point is there a suggestion on how to find where the placeholder is and where the issue is without having to go through all the run around?

One fix - I was able to open the hyperlinks window, delete all of those, then restart placing the code in my document one by one , and it worked, but there should be another way.

Check for any special characters in the header names of the source document. That can maybe help you whittle down the issue too. 

Try pasting them a few at a time into a new document, and trying a merge from the same data. As soon as it doesn't work, you can easily narrow down the one that stopped it. Resolve that placeholder in your main document, and if it still doesn't merge, repeat the process with the remaining placeholders until you find all of the culprits.