I'm a new comer to Grails and presently stuck in the following problem: I've two models "BasicData" and "ExtendedData". In BasicData.groovy I've defined the 1:1 via extended = ExtendedData

Now I've read will be able to simply save both of them by invoking the BasicData Controller only factor I recieve is really a nasty Exception message without any real explanation from the error.

You need to define the 1:one in BasicData by doing this:

class BasicData terms

Are you certain this is the way you have carried out it? Also, based on your needs you may have to include a belongsTo attribute in your soul ExtendedData class. Find out more about 1:1 associations in section here: http://grails.org/doc/1..x/guide/5.%20Object%20Relational%20Mapping%20(GORM).html