This is a general error message by StimPlan. It can be caused by various reasons. From this message only, it is difficult for us to troubleshoot. We need more information to find the root cause. In order to reproduce the problem on our end, we need at least these two items from you:
1. If possible, please share us with the problematic STP file. If you are concerned on confidentiality, you may need to remove the field name, formation names, well name, etc. from the STP file beforehand.
2. Please provide the StimPlan version information. It can be found at the StimPlan top bar menu --> Help --> About Stimplan... Capture the window for us as shown in the example below.
With the STP file and the StimPlan version, we will try to reproduce the problem on our end and start from there.