I was in school and writing things off the board when suddenly this error occured.
This has recently come up. Check here: https://community.ptc.com/t5/PTC-Mathcad-Questions/Unknown-Failure/m-p/160130
Please attach your Mathcad Prime worksheet (in archive ".zip" format) to the message.
Well here is my file. I tried to reboot my Computer and closed and reopened the file but this didn't work out either.
Interesting. When I opened the file (using P4) it showed the same errors. Deleting the symbolic arrow and re-applying the symbolic arrow corrected the error. I don't know why.
Take the following steps (your worksheet works fine in Mathcad Prime 3.1 with this tip):
1. Uncheck "Multithreading" option from "Calculation" tab --> "Calculation options".
2. Click on "Calculate" and recalculate your document.
1. What version of Mathcad Prime do you use?
2. Please send your issue for a PTC's tech support by using "Mathcad Support Center": https://support.ptc.com/support/mathcad_supportCenterOpt.htm
Nothing you did was wrong (apart from using Prime instead of real Mathvad - but I guess you had no choice).
It looks like you ran into a Prime bug which still is not fixed.
Is it cured, when you save the sheet, close Prime and then reopen the sheet?
The last time this error came up here, reopening the sheet "solved" the problem.