If the action "Set item permission" is used to set a user or group permission to a SharePoint integrated permission level, the workfow can fail without exact error message on multilanguage environments.
Integrated permission levels are for example: Full Access, Contribute, Read, View Only.
It looks like Nintex Workflow uses string comparison to set item permissions.
While a workflow designer in an english interface can select the dropdown item "Full Access", the workflow designer in a german interface would select "Vollzugriff".
Because "Vollzugriff" != "Full Access", the permission cannot be set.and the workflow will fail. Nintex will not correctly catch the error and no error message is logged.
The test environment was a SharePoint 2013 on a german Windows Server 2012.
The user interfaces of the workflow designer, the workflow publisher, the workflow initiator was English and the workflow action item had the English title "Set item permission".
However it was not possible to set one of the integrated permission levels.
The problem can be reproduced in our environment.
Is this already a known issue?
Yes, this is a known issue, due to SharePoint's behavior, as it is expecting a Permission value in site Language,
for example if your site is in English, SharePoint expects "Full Control" and if your site is German or Japanese or any other language, it expects, "Vollzugriff" or "フル コントロール".
so far I believe this issue is resolved already, but if you are still facing the issue, please report it to Nintex Support.
I think in the meantime the error should be solved. What Nintex version you are using?
Here is the answer (from 3/18/2014) to the support case I opened in march 2014:
The development team have reviewed this case and provided the following information.
If you are having issues with Set Item Permissions in a non-English site, you should install the 22.214.171.124 hotfix which was released to fix this issue.
Please be sure to also download and reference the version history document, which has the update instructions on pages one and two from http://nintexdownload.com/sl/supportfiles/NW2013_version_history.pdf.
If DLLs are missing from the GAC, it indicates that either the SharePoint solution package has not been deployed, or it has been deployed and has errored.
Note that SharePoint handles the copying of DLLs to all WFE servers in the farm. This is standard SharePoint deployment functionality.
Another thing for you to check is that the server missing the DLLs needs to be running the Web Application role. If it is not, SharePoint will not copy the DLLs to that server.