Have you tried to do this from command line
request tech-support dump
you can look at show jobs all, and find the error'd job id number and perform a "show jobs id xxxxxx" to see the message.
Else, contacting support directly.
Perhaps a software upgrade, a FW reboot, a restart of the management plane, etc.. any could be some you could do to help troubleshoot the issue and move it forward towards resolution.
check if there's still space available on the disk, and try to clear up some space if needed: https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClaJCAS
then try again
alternatively try running it from CLI:
tftp export tech-support to 192.168.27.7
Click Accept as Solution to acknowledge that the answer to your question has been provided.
The button appears next to the replies on topics you’ve started. The member who gave the solution and all future visitors to this topic will appreciate it!
These simple actions take just seconds of your time, but go a long way in showing appreciation for community members and the LIVEcommunity as a whole!
The LIVEcommunity thanks you for your participation!