Hi, I was going through Exception Handling described in

Hidden/undocumented SAIL function - try-catch in Appian SAIL:
try (
[CODE],
"Code failed"
)

EDIT: Please exercise care when using this function, as I was advised by Josh it may not be maintained by Appian:

community.appian.com/.../is-there-a-way-we-can-catch-exceptions-in-sail-form-something-like-try-catch

I would suggest two work around approaches as below,

1. you can set Exception Timer on node, let say set it for 10 minute, attach a script task as link to your exception which update your boolean variable (E.g blErrorOccured) as true and link this script task to your user input task. On user input task, you can easy show message base on value of your set variable (ri!blErrorOccured).  

2. You can add AND gate after start event and wait till some time, like 2 or 3 hour (more than usual time your process takes to complete), if your process don't complete in that time frame, it means some error has occurred, you can display an interface with proper message. 

Regards,

Simple Shah

simples533 - 

I don't recommend an exception timer for error handling on a specific task. 
It's not reliable. 
More detail on this position is in this post.