This error will pop up when your text(...) datatype in the Writer allows for less characters then there are in the Reader.
Example:
Table1 Column_Name text(300) going into Table2 Column_Name text(255) will work as long as the records in Table1 don't exceed 255 characters, if they do then you have the bad value error.
It is also possible that you are trying to put an integer data type into a double, or the other way around.
It is due to the nature of ESRI Geodatabase API, if you use the Arc Objects format for your writer then the records will be truncated instead of being omitted. Be careful though, Arc Objects is a 32 bit technology, so it is not supported in 64 bit FME Workbench, you will have to use the 32 bit version for that.
If you have to use the Esri Geodatabase API for your project then I have a workaround solution for you to find out which rows have the bad values exactly, as it is not yet a thing in FME. This will help you with troubleshooting the problem columns. Ask me if you need more information on that.
Thank you,
Kostia