When creating an InDesign merge document, be sure to select the fields from the list that is generated after you select a data source. Double click on the field name in the list to place it into your document. Don't try to freestyle by typing them manually. I often get the placeholder error when opening a previously saved file that has outdated (or invalid) field names. All it takes is one bad one and the merge will fail even if all the others are valid. When in doubt, run a test by placing the merge fields into a completely blank document and trying to run preview from there. Remember, when you get the placeholder error, the problem is your InDesign layout, not the data file. Hope this helps.
When creating an InDesign merge document, be sure to select the fields from the list that is generated after you select a data source. Double click on the field name in the list to place it into your document. Don't try to freestyle by typing them manually. I often get the placeholder error when opening a previously saved file that has outdated (or invalid) field names. All it takes is one bad one and the merge will fail even if all the others are valid. When in doubt, run a test by placing the merge fields into a completely blank document and trying to run preview from there. Remember, when you get the placeholder error, the problem is your InDesign layout, not the data file. Hope this helps.