Hi Mohamed,
There might be several reason for this. Some of them i encountered.
1. It might be possible that your inbox in the back-end having a large amount of work-items and UWL system is not able to retrieve all of them into inbox and giving dump. You need to delete the workitems from SWIA and lower the count.
2. It might be possible that RFC authorizations are not with the user. Thats why its getting into error while calling RFC to fetch the workitems.
Kindly check and see , what type of error it is.
Thanks
Rakesh