&1 is not a valid field name for table "&2"

What causes this issue?

At least one of the components of the file you are about to import
contains a reference to an invalid data object. A data object is an
entry maintained in transaction MDCMODEL.

System Response

This error message is raised because it is essential that each value of
your file contains a valid reference to a valid data object and a valid
field of those data objects, respectively. The import cannot be carried
out when this kind of invalid reference was found.

How to fix this error?

Check each header entry of your file, which is each cell of the first
line in case your file is a Microsoft Excel document, or a single value
of the first line when your file is a CSV file.
All of those values need to either refer to a data object explicitly by
separating its name from the field's name by the "-" delimiter, or
implicitly by letting the sheet's name start with the data object's name
(Microsoft Excel document), or letting the CSV file's name begin with
the data object's name (CSV file).
In case the table name mentioned in this message is empty, your file
might contain one or multiple invisible characters, or a space. This
mainly occurs in MS Excel documents. If the complete column mentioned is
empty, click on the column's header to select it, and right click the
header and choose "Delete" in the context menu.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.