Issue
This error message usually appears when there is a datatype mismatch defined within a Formula. An example of this is where the result of the Formula is a string but the target field you are trying to update is of type Whole Number.
Resolution 1
The first resolution of this issue is review the formulas you have defined for the entity that threw the error message and try to find a datatype mismatch between the result of a formula & its target property.
Resolution 2
The next resolution of this issue is enabled Dynamics CRM 2011's native tracing. The following KB article from Microsoft explains how to do this.