Issue with SSL cert on CNmeastro Version 2.4.2-r8

We are having an issue with the installation of the SSL cert.

According to this link

and the help information in the import section.
" Import a Signed Certificate generated from a CSR or a Signed Certificate along with its Key (optionally encrypted). For either choice, please make sure all files (including Signed Certificate, Intermediate Certificates, and optional Key) are concatenated into a single PEM encoded file before uploading. For certificate chaining bundle, the server certificate must appear before the chained certificates in the concatenated file."

All of this says to concatenate the information into a .PEM file.
And this was done.
However, we then select ‘Import Signed Certificate and New Key’
And then select the PEM file.
The moment that is done, it pops up with an error saying ‘Please select .crt file only’

What is being done wrong here.
We follow the instructions and still it will not.