Installing certificate not working

hello all,
i'm trying to install SSL to our helpdesk web, and it fails with the below error

My steps are hereunder:

step 1:
keytool -genkey -alias helpdesk.xxxxxxx.com -keyalg RSA -keysize 2048 -keystore sdp.keystore

Password: xxyxyxyxyx
*.xxxxxxx.com ( we use wildcard cert)

step 2:
keytool -certreq -alias helpdesk.xxxxxxxx.com -file keyshimy.csr -keystore sdp.keystore

step 3:
download th certs.zip from digicert site

step 4:
keytool -import -trustcacerts -alias root -file TrustedRoot.crt -keystore sdp.keystore
keytool -import -trustcacerts –alias intermediate -file DigiCertCA.crt -keystore sdp.keystore
keytool -import -trustcacerts -alias helpdesk.xxxxxxx.com -file 1star_xxxxxxxxxxx_com.cer -keystore sdp.keystore

After it fails with "keytool error: java.lang.Exception: Failed to establish chain from reply"

have you any ideas ?

Thanks :)