Machining PowerPac: Failed to Activate. Index was out of range. Must be non-negative and less than

Amol
Amol India
Dear All,
I am using RobotStudio 2019.4 with the Machining PowerPac 2019.5 where we got the following cryptic message and the powerpac refuses to start on these stations. 
"Machining PowerPac: Failed to Activate. Index was out of range.  Must be non-negative and less than the size of the collection. Parameter name: index"

This message is coming frequently

They were working fine one day and then the next, they won't open the powerpac.

other stations open and work fine

Please help in this issue