IBM Cognos User Manual page 302

In a PowerCube group, you have tried to omit the dimension containing the level
that defines the group.
Procedure
You cannot omit this dimension. If you want to omit a portion of the dimension,
use a custom dimension view. Be aware, however, that omitting one of the
categories that defines a cube in the group by using the Exclude or Cloak action
will cause that cube to be deleted from the group.
TR2001
The main dimension is required in the time-based partitioned PowerCube
cube_name. It has been omitted for custom view view_name.
In a time-based partitioned cube, you have tried to omit the dimension containing
the level that defines the cube, for the specified custom (security) view.
Procedure
You cannot omit the entire dimension. If you want to omit a portion of the
dimension, create a custom dimension view.
TR2002
This dimension cannot be omitted for this custom view because it is the main
dimension for time-based partitioned PowerCube cube_name and the custom view
has been added to that cube.
For a custom (security) view in a time-based partitioned cube, you have tried to
omit the dimension containing the level that defines the time-based partitioned
cube.
Procedure
You cannot omit this dimension. If you want to omit a portion of the dimension,
create a dimension view instead.
TR2306
You have specified a label column. Please specify an associated column also.
This message suggests that you may have inadvertently deleted the associations or
roles from a Level property sheet.
Procedure
To resolve the problem, ensure that the source information is complete and correct.
TR2307
A level was expected but not found. Either you have referred to a level by an
object name or object identifier that Cognos Transformer is unable to locate, or you
have not referenced the level.
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IBM Cognos Transformer Version 10.1.1: User Guide