'cabal install --only-dependencies' fails

mongoEg.cabal

-- Initial monogEg.cabal generated by cabal init.  For further 
-- documentation, see http://haskell.org/cabal/users-guide/

name:                monogEg
version:             0.1.0.0
synopsis:            mongoeg
-- description:         
license:             GPL-3
license-file:        LICENSE
author:              fizz
maintainer:          fizz
-- copyright:           
-- category:            
build-type:          Simple
-- extra-source-files:  
cabal-version:       >=1.10

executable monogEg
  main-is:             Main.hs             
  -- other-modules:       
  -- other-extensions:    
  build-depends:       base >=4.7 && <4.8, mongodb
  -- hs-source-dirs:      
  default-language:    Haskell2010

shell output

$ cabal install --only-dependencies
Resolving dependencies...
cabal: Could not resolve dependencies:
trying: monogEg-0.1.0.0 (user goal)
next goal: mongodb (dependency of monogEg-0.1.0.0)
Dependency tree exhaustively searched.

Note: when using a sandbox, all packages are required to have consistent
dependencies. Try reinstalling/unregistering the offending packages or
recreating the sandbox.