For a current project I am working with Exchange 2019 and for OWA we want to implement Office Online Server. I did this in the past and blogged about it (Install Office Online Server 2016) so I thought it should not be a big deal.

Installed Windows 2016, installed prerequisite software, configured an SSL certificate, installed Office Online Server and created a new Office Web Apps farm.

After testing the https://fqdn/hosting/discovery and configured the organization configuration everything must be good.

When opening an attachment in OWA I do see the OOS environment, it tries to open a document and then generates this error:

“Sorry, there was a problem and we can’t open this document. If this happens again, try opening the document in Microsoft Word.”

When opening an Excel attachment, I get the following error message:
“Unable to open the file. We couldn’t find the file you wanted. It’s possible the file was renamed, moved or deleted.”

I know Office Online Server is sensitive for SSL certificates, but this was a regular Digicert certificate. Name resolution was fine as well. But the check https://fqdn/op/generate.aspx failed as well with the following (pretty useless) error:

“Server Error. We’re sorry. An error has occurred. We’ve logged the error for the server administrator.”

Unfortunately, nothing useful in the eventlog, or in the ULS logging on the Office Web Apps server. Asked colleagues, but they had only experience with Exchange 2016 and OOS.

After two days of searching, fiddling with the server, checking .NET versions (Windows 2016 comes with a newer version of .NET then required by Office Online Server), rebuilding the Office Online Server several times I realized it might be a TLS 1.2 issue. Exchange 2019 is using TLS 1.2 only by default, whereas Exchange 2016 can use multiple versions of TLS.

So, on the Windows 2016 server with OOS, I enabled strong cryptography in .NET and disabled older versions of TLS on Windows to fix the issue.

To enable strong cryptography in the .NET Framework, add the following registry key:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft.NETFramework\v4.0.30319]
"SchUseStrongCrypto"=dword:00000001

To disabled older versions or TLS, add the following registry keys:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\PCT 1.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\PCT 1.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
@="DefaultValue"
"Enabled"=dword:00000000

After rebooting the Office Online Server, it worked as expected.