Remote Desktop Gateway connection intermittent with certificate error

When attempting to remote desktop into an RDS gateway server, we are receiving the following error:

"Your computer can't connect to the remote computer because the Remote Desktop Gateway server's certificate has expired or has been revoked. Contact your network administrator for assistance."

The server is Windows Server 2008 R2, and we are positive the SSL certificate is valid. RDWeb is working fine and can be used to remote desktop other computers on the network without issue.

We have already tried reinstalling the RDS role and had the certificate reissued. We have been seeing this issue connecting from Windows 7, Server 2008, and from the Microsoft Remote Desktop app from iTunes. Oddly enough, if you keep trying, the connection will eventually succeed after a random number of times. On some systems, the connection succeeds nearly 100% of the time.
brainsurf1Asked:
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VB ITSSpecialist ConsultantCommented:
On the RD Gateway server, open Administrative ToolsRemote Desktop Services > launch the Remote Desktop Gateway Manager > right click on your server name in the left pane > Properties > click on the SSL Certificate tab > verify that the correct certificate is showing underneath The following certificate is installed on <SERVER NAME>

If it's showing the old certificate that has expired, click Select an existing certificate from the RD Gateway SERVER Certificates (Local Computer)/Personal store > then click on the Import Certificate button > select your recently renewed certificate > OK > RD Gateway Manager show now show the correct certificate. Test the RD Gateway again.
RD-Gateway-SSL-Certificate.png
If you still don't see the new SSL certificate, restart the Remote Desktop Gateway service (NB: this may kick out everyone currently logged in via RD Gateway).

Let me know how you go.
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brainsurf1Author Commented:
We have already imported a valid SSL certificate into the RDS gateway MMC. This certificate was recently purchased and doesn't expire for several years.
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VB ITSSpecialist ConsultantCommented:
What happens when you open the Certificates MMC for the Local Computer/Personal store and double click on the new SSL certificate? Does it show up as valid?
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brainsurf1Author Commented:
The certificate does show up as valid.

Certificate MMC
Certificate MMC 2
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VB ITSSpecialist ConsultantCommented:
I'm assuming you deleted the old expired certificate from the store as well once it was replaced? Sorry, have to cross off the standard stuff first.

Do you see any warnings/errors in the logs when you attempt to connect remotely via RD Gateway?
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v_2abhis2Commented:
Hi,

Could you please check the certificate revocation list for Rapid SSL, you will find the URL on the details tab under the field CRL Distribution points.

Browse the url, download the CRL file and open the certificate revocation list tab, now check the Serial Number of the certificate issued to you and make sure its not there on the CRL list published by Rapid SSL

As Rapid SSL might have revoked your certificate because the certificate issued to you may be SHA-1 and they might have upgraded to  SHA-2 (SHA-256)  or higher security algorithm.

As Google (Chrome) started displaying errors on the padlock icon for any website using SHA-1 SSL certificates from November, so everyone is upgrading their infrastructure to SHA-2

Review the attachment for example

Thanks
Abhishek
CRL.PNG
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brainsurf1Author Commented:
Thanks everyone for your responses. Abhishek, I downloaded the certificate revocation list from the URL provided in the details for the certificate. However, I was unable to find the serial number for our certificate in the revocation list.

One complication to this is that we have actually just reissued our RDS gateway certificates to use SHA-256 after they were previously all SHA-1. The certs were working fine until recently, but we have deleted the old certs from the server (issue persists).
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brainsurf1Author Commented:
I believe I have resolved the issue: Previously, we were using an SSL certificate with 4096 bit length and SHA 256. I reissued the certificates using 2048 bit length and SHA 256. We are no longer seeing this issue. I am guessing some clients had issues reading the larger bit length, although I am no expert in this field.
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brainsurf1Author Commented:
The server was not improperly configured. Our clients likely had issues with a larger bit length in the SSL certificate.
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Windows Server 2008

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