CEF rendering exception - "Buffer cannot be Null" Error in NP report preview with Qlik Sense Connection

Juli_K — Tue, 11 May 2021 16:54:22 GMT

June 2018 version for NPrinting when adding image in NPrinting PowerPoint report, the error is thrown.:

Failed generation of report 0c7c6575-d015-4703-a7e1-6a1d74bf4805 for user 3788bde1-f9db-47e8-8c16-112e5fabf2a4. ERROR: System.Exception: Object <objectid> of Sense app <senseAppID> failed to render. ERROR: Buffer cannot be null.

Restarting the NPrinting services corrects the issue periodically.

Environment:

17 platform

Resolution:

Upgrade to at least November 2018.

A vast number of other CEF rendering exception variance have been resolved after the release of June 2020. For more details see Advanced troubleshooting of the GRPC and or CEF Error Issues:

The first thing to check is that the connection in NPrinting is pointing to the Qlik sense Default proxy.
Go to Qlik Sense QMC > Virtual Proxies. Is there a prefix for the default proxy?
If so, be sure that this has been added in the NPrinting connection. The "Proxy address" in the connection should look like https://ServerName/Prefix

If the NPrinting connection is correct, the problem may be related to a known issue. Instead of restarting the NPrinting services in the event of a error being reported when adding an image perform the workaround below.

Workaround:

Find a failing task
Disable the engine from Engine manager page and wait until it goes Offline
Re-enable the engine and wait until it goes Online again
Run the failing task again

If that works, then we have a setting recommended to be entered in the scheduler.config file (ProgramFiles\NPrintingServer\NPrinting\Scheduler):

1. Stop NPrinting Scheduler and NPrinting Engine(s) services

2. Open scheduler.config (in scheduler installation folder) file

3. Add the following line within the appSettings section (the line just before the closing </appSettings> is ok):

4. Save the changes (pay attention that the file should be named scheduler.config, not scheduler.config.txt)

5. Restart the scheduler service and the engine service(s)

What this key is for?

Per R&D, it essentially tells the scheduler to request a "close all Qv/Sense connectors (that we call resolvers)" to all NPrinting Engines when there are no more requests to resolve.

This forces the engine to shutdown all connections to QlikView/Qlik Sense servers, usually freeing up some RAM on the NP engine machines but most importantly avoiding some session timeout related issues.

Items to be aware of:

Sessions are closed immediately when there are no more requests to resolve. If a user will ask for a preview immediately after this will force to start a newly created connector/resolver and this could take several seconds (usually more on Qvs connections than on Sense ones).

The option is lost when an upgrade is performed

Please NOTE : R&D recommends avoid using it on NPrinting + QlikView installations because it is very rarely needed and the impact on performance could be noticeable. On the contrary usually not a noticeable degrade with Sense (and if it happens it is due to a very high number of Sense apps in the Sense server and/or slow internet connection).

Cause:

Defect IDs:

OP-7828
OP-8010 / OP-8316

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CEF rendering exception - "Buffer cannot be Null" Error in NP report preview with Qlik Sense Connection

Resolution:

Workaround:

Cause: