I followed your instruction and uploaded the Root cert. The error is still showing, does the PCKS12 file need to be removed and re-added?
If it is a multiple chain cert with Root and Sub CA's, try only adding the identity and immediate sub CA to the pkcs12 file. For example, if the chain is like this:
RootCA---> SubCA1---->SubCA2---->Identity Cert
Only add the SubCA2, identity cert and private key to the p12 file and test.
Also, to troubleshoot, run the following debugs on the diagnostic CLI when importing it via the FMC:
debug crypto ca 255
debug crypto ca messages 255
debug crypto transactions 255
I uploaded only the SubCA, the identity cert, and the private key and received the same error. I ran the debugs but didn't receive anything during the upload.
Uploading only the Sub-CA, Private Key, and Identity cert to the PKCS file resolved the issue. Any reason why it would cause a problem to keep the root cert in the file?