If a simulation fails because of a math fault — for example, a negative argument to a log function — Embed displays a dialog stating the nature of the error and highlights the offending block in red. To reset the error condition, point to the offending block and right-click. If the offending block is encapsulated within one or more compound blocks, each compound block is also highlighted in red. Note that you’ll have to drill into highlighted compound blocks to find the offending block.
If multiple blocks contain errors, use Edit > Clear Errors to clear all the errors.