Error – External table is not in a valid format when you access an excel file

There could be many reasons for this error; one of them is that the file is locked by another user, for example your file is on a shared drive and another user has the file opened, or the file was uploaded or created by another application and the application still has a lock on it, if this was a one time load then you just need to copy the file and load the copied version of the file.

In case this was an automated recurring process then every time you need to copy the file to another folder, load the copied file then delete it.

hope this is helpful!