I recently was getting an error while trying to install a CRM 2011 solution at a Customer site. I was getting and error message stating “invalid fields” on a specific custom entity. After looking at the download log in Excel, I found the issue. I had created a field with the wrong data type and had successfully already imported the solution on my clients system. On my development copy, I deleted the field and recreated it with the correct data type but with the exact same name – that was the field that was preventing the solution import from working. The solution import process would not change the data type but instead raised the error message. Once I deleted the field on my client’s machine, the solution imported successfully.