Wildcard SSL Comodo certificate installation problems

[RubenV]

Hi

Yesterday I bought a wildcard certificate for my domain (lets use example.be here)

Domain:
example.be

Aliases:
*.example.be

I did the required steps:
1. Generate CSR
2. Copied the SSL Key (private key)
3. Bought the Wildcard Comodo certificate
4. Now I received 4 files and I tried to install them like I read on this forum:
- AddTrustExternalCARoot.crt
- COMODORSAAddTrustCA.crt
- COMODORSADomainValidationSecureServer.crt
- wildcard_example_be.cer
5. I copied the next text:
- SSL Certificate -> wildcard_example_be.cer (=> I receive a cer file and not a crt file?)
- SSL Key -> my copied SSL key (starts with -----BEGIN RSA PRIVATE KEY----- and ends with -----END RSA PRIVATE KEY----- )
- SSL Certificate Authority / Intermediate (all together in the textbox)
--> COMODORSADomainValidationSecureServer.crt
--> COMODORSAAddTrustCA.crt
--> AddTrustExternalCARoot.crt

Now I get every time the error
SSL Certificate key pair is not valid

I installed already 50 SSL certificates, but no wildcard certificate on Vesta.
What I'm doing wrong?
I already read through all the forum (here and here)

Thanks in advance!