Does the error message simply contain a generic error message? It would be something like: 'An error has occured while processing your request. Please contact your system administrator.' If that is the case, it is likely there is some error in your microflows or page design behind the scenes. This error popup will always occur if there is an exception in the underlying model. The only way to make this go away is to fix the error.
To find the cause of your error, run this project in your local modeler, recreate the error and then look at the console log. This should provide you with more detail about what is causing your exception. Only by narrowing down the cause of your error can you come up with a specific fix.
See this how-to on finding error causes that will give you the tools you need to get started:
Here is another how-to on debugging microflows that may help: