Q:

Formula Field Deployment to Production

I am trying to deploy a couple of formula fields from sandbox to production but I am receiving this error:
The formula references fields across 11 relationships while only 10 are allowed.
Now I know for a fact this is not the case. The formula is very simple on traversing one level deep. There is a lookup field on the object. I am using that relationship to display a field from that object via a formula field. So basically it looks like this:
Custom_Object__r.Custom_Field__c
I have this issue with two formula fields. Any ideas why I am getting this error while moving to production?
Also using the Force.com Migration Tool

A:

Echoing @Birthus but with an additional wrinkle:
Since you didn't report the error in sandbox, it is possible that you started with 10 cross-object relationships from your object Foo to other objects: obj1__r.xxx, obj2__r.yyy, ...obj10__r.zzz then you deleted one of the obj1 ... obj10__r and added an eleventh relationship obj11__r.www.  Your sandbox won't complain. 
This can be challenging at deployment time as the addition of the 11th and the processing of the delete of one of the first ten doesn't happen in the same sequence as you expect. I believe this is because the field that was deleted referring to the 1-10th relationship needs to be Erased from the PROD org before you can deploy.  I know when faced with this before I had to first get down to 9 relationships before adding my tenth - hence a two step deployment.
That said, an easier way out if you can wait, is to file a support ticket with SFDC who I believe can increase the limit to 15 from 10 (cross object relationships)

A:

The limit is per object, so you must have a number of other formulas that also reference cross-objects. You must not have all the other formulas in your sandbox.
To find out what other formulas you have that are referencing cross-objects, try creating the formula manually in production. When you get the error, you will also get a link to show you all the other references. That's the only way I know how to find them easily.
(I also agree with crop1645 - you can contact support to get a limit increase)

