Dear Allan,
In case you haven't seen it, the following video introducing the IPH trough model might be helpful:
sam.nrel.gov/node/74797
In general, when you change design parameters like the loop HTF temperatures, you may need to adjust other parameters accordingly. You can explore the outputs to see if the operating temperatures and pressures are what you expect, and then make adjustments to inputs.
If you need more help, please tell me what specific error you are seeing, and if possible attach your .sam file (edit your original post above) so I can better understand what you are describing.
Best regards,
Paul.