Failed to evaluate the calculator expression

Error Message

This error message is returned after clicking Evaluate on the Raster Calculator dialog box:

"Failed to evaluate the calculator equation"

Cause

There are several causes for this problem:

• There is a syntax error in the calculator expression.
• The extent and cell size of the input raster is different than the extent set for the analysis results.
• The expression is not evaluated if there are carriage returns before or after the expression.
• The Raster Calculator is case sensitive.
• There are too many open grids. There is a limit of 50 open rasters of the grid format at any one time.

Solution or Workaround

Some of these issues have been addressed in supported versions of ArcMap.

The corresponding workarounds for the above causes are:

• Check the syntax. Type Map Algebra in the index of the online Help system for information on Map Algebra and its syntax.
• Make sure the extent and cell size of the analysis result is set appropriately in the Extent and cell size tabs of the Options dialog box. The extent of the analysis results should be set the same as, or encompass, the extent of the layer used in the Raster Calculator.
• Do not use carriage returns in the expression. Allow the expression to word-wrap if it is lengthy. This has been addressed in supported versions of ArcMap.
• Make sure the layer name typed into the expression box case matches the name of the layer in the Layers list. For example:

Layer name: Elevation
Expression typed: slope([elevation]) 

This expression will not work. The first letter of "elevation" should be capitalized. This problem has been resolved in supported versions of ArcMap.

• Remove any un-needed grids from the ArcMap Table of Contents. The total number of open grids, including the one being created by the Spatial Analyst function, cannot exceed 50.
  • This limit does not apply to non-grid rasters. A workaround is to convert grids to rasters in ArcCatalog with the Export > Raster To Different Format option.