Error "work Item Cancelled"

Can you check the assignment of the Script task?
Eg: It is assigned to the Process Initiator and the user doesnot have the necessary privileges to execute the rule.
This also happens when the process instance is initiated and the process initiator's User ID is disabled.

@sanjays the Script task run as automated activity started by process Initiator.. and the Process Initiator's User ID is disabled indeed.. the strange thing is that every node (including other script tasks) is assigned to process initiator, but but only two of them are failing.. do you thing it could happens that only some node may fails?

I think so.
When I have seen this issue, Process instance is created by the Initiator.
When the User ID is disabled and next day after that, when some other user is working on tat task, I have seen this issue.
I have edited the process instance, changed the swimlane assignation from initiator to designer and it worked.
You have to take care of the User Input Tasks though to make sure that it would not get assigned to some other user instead of the user working on the task.

Note: I have seen this issue for a Sub Process call (as I dont have a Script task when the issue occurred)

I have faced this issue once, I have deleted and redesigned the particular script task, it worked!

Cause
This issue typically occurs when the impacted process is running under a deactivated user account. Due to this, a permissions check fails when trying to execute certain nodes, for example, User Input Tasks and some unattended activities. This issue has been reported to the Appian Product Team. The reference number for this issue is AN-46187.

Action
If the error is occurring in a sub-process, ensure that the sub-process node in the parent process is not set to run as the deactivated user. For example, if the parent process was designed by a deactivated user, set it to run as the initiator. If the parent process was initiated by a deactivated user, set the sub-process to run as the process designer.
If the error is occurring in an unattended activity, repeat the steps from the above on the "Assignment" tab of the failing unattended activities of the Process Model.
If the error is occurring in an User Input Task or another attended activity, ensure that the user is not referenced in the assignment of that node, cancel all pending activity on the model, and restart the node as an active user.
Workaround
If all of the steps in the "Workaround" section fail to resolve the issue, temporarily reactivate the deactivated user account and add the user to a group, then remove the user from the group before allowing the process to complete. In order to ensure the deactivated account cannot be accessed by the user who it belonged to, follow the steps below:

Change the e-mail address to something other than the user's actual e-mail address.
Reset the password via the Admin Console.
Affected Versions
This applies to all versions of Appian.

Work Item Cancelled>> error occurs when a process lane property or task has setting as Run whosoever has designed/Run whomsoever has started and that account has deactivated.

Below 3 solutions i have tried and all worked.

1. you can reactivated user and please ask him/her to login other wise it wont work or you try loggin if that account exist.

2. For instances to make them run please update lane/task assignments(it can be failling on both as per the assignment) to other one like if it is  Run whosoever has designed make it to Run whomsoever has started and vice versa.

3. please go to prcess models published by that deactivated user and republish all then can trigger a new process.