Unable to merge feature classes using the Merge tool

Description

The Merge tool combines multiple input datasets into a single output dataset. In some instances, merging feature classes using the Merge tool fails and the following error is returned.

Error:   
The spatial index grid size is invalid.

Cause

This error usually indicates that there are inconsistencies in the spatial index grid values of the feature classes to be merged.

Solution or Workaround

To resolve this issue, recalculate the spatial index of the feature classes before merging. To do this in ArcMap, follow the instructions provided below.

1. Delete the spatial index from the feature classes.
   1. Navigate to ArcToolbox > Data Management Tools > Indexes, and double-click Remove Spatial Index.
   2. Select the desired feature class in the Input Features field, and click OK.
      
      
       
   3. Repeat steps 1a and 1b on other feature classes to be merged.
2. Recalculate the spatial index for the feature classes to be merged.
   1. Navigate to ArcToolbox > Data Management Tools > Indexes, and double-click Add Spatial Index.
   2. Select the desired feature class in the Input Features field, and click OK.
      
      
       
   3. Repeat steps 2a and 2b on other feature classes to be merged.
3. Run the Merge tool.
   1. Navigate to ArcToolbox > Data Management Tools > General, and double-click Merge.
   2. Select the desired feature classes in the Input Features field, and click OK.
      
      
       

      Note:
      Alternatively, use the Dissolve tool to merge the feature classes, but do not select any fields to dissolve. For more information, refer to ArcMap: Dissolve.