The parameter callback_error specifies the name of the JavaScript method to be used as call back function for error codes in case of errors.
The parameter's structure: MyCallbackError(ERRORCODE)
ERRORCODE: contains the error code (the code number if return_error_codes=true, else the error code itself, e.g. SERVER.FATAL.NO_PROJECT_CONFIG) in case of errors.
Note: The methods name MyCallbackError is just an example as well as the parameter's names.
Example:
http://w-vpc-sw-w7-e:8080/WebOffice_LatestBuild/client_mapwidget/default.jsp?baseURL=http://w-vpc-sw-w7-e:8080/WebOffice_LatestBuild&project=WebOffice_SampleProject&width=600&height=400&callback_error=MyCallbackError&return_error_codes=true