Unmapping File Content
When you setup DSS tasks to download folders/files from Dropbox to your physical system and vice versa, it is mandatory to unmap the file content in field mapping tab. If you do not unmap the file content, the DSS task will not run as expected, an invalid datatype conversion error appears.
To unmap the file content follow the instructions given below.
In Field Mapping Tab, select FileContent field.Click

(clear expression/lookup) to unmap file content.
After you have unmapped the FileContent, the field appears as shown in the above figure.