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Your LimeSurvey version: Version 3.28.42
Own server or LimeSurvey hosting: own server
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Hello!
I am having issues with saving an unfinished survey and loading the answers for resuming later and would appreciate your help. 
When trying to save the answers, this seems to work just fine and I also get a confirmation that they were saved successfully. I can even find the saved entry under cached. However, when I try to load the entry and resume with filling out the survey at a later time, I get the following error (see attachment). 
I believe that the issue is that the survey contains several "data-upload" questions which probably cannot be saved in the cache, because I tried removing those questions from the survey as a test and in that case it worked to load the answers later. However, unfortunately I do need to keep the data-upload questions in the survey, so I would appreciate any suggestions for a workaround to enable saving and resuming later too. 
One more info: The survey will be conducted as a closed survey, only sent to a predefined list of participants that can access it via personalized access keys.
Thank you! 

With kind regards
Flavia 
 

If it is a closed survey (with tokens), you can activate token-based response persistence to allow respondents to return to the survey with the original invitation link.

- www.limesurvey.org/manual/Participant_se...response_persistence

Thank you for your help! Indeed this seems to work!