When computing a model using the Explicit (SWMM) solver, it fails, generates a red user notification stating "The SWMM engine failed during the calculation..." and in the SWMM Calculation Summary, the following error is seen:
"Error 211: Invalid number"
This issue can occur in a number of different situations where there is an issue with the data entry for elements.
First, make sure that you have the latest version of SewerGEMS or CivilStorm installed, as well as the latest patch set. You can use the instructions at this link to find the latest installation file.
If that doesn't help with the issue, check the data input for the element label referenced in the error message.