When running npm install as part of my pre-build script, the command exits with an error.

Here is the relevant logs:

[19:15:12] npm install
[19:15:12] npm WARN package.json Heartbeat@0.0.0 No description
[19:15:23] npm WARN package.json Heartbeat@0.0.0 No repository field.
[19:15:23] npm WARN package.json Heartbeat@0.0.0 No README data
[19:15:23] npm WARN optional dep failed, continuing imagemin-jpegtran@0.1.0
[19:18:13] npm WARN optional dep failed, continuing imagemin-optipng@0.1.0
[19:18:21] npm WARN optional dep failed, continuing imagemin-pngquant@0.1.3
[19:18:24] npm WARN optional dep failed, continuing imagemin-gifsicle@0.1.1
[19:18:26] npm ERR! EEXIST, open 'C:\Users\appveyor\AppData\Roaming\npm-cache\695421b6-adable-stream-1-0-32-package-tgz.lock'
[19:18:32] File exists: C:\Users\appveyor\AppData\Roaming\npm-cache\695421b6-adable-stream-1-0-32-package-tgz.lock
[19:18:32] Move it away, and try again. 
[19:18:32] 
[19:18:32] npm ERR! System Windows_NT 6.2.9200
[19:18:32] npm ERR! command "C:\\Program Files (x86)\\nodejs\\\\node.exe" "C:\\Program Files (x86)\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "install"
[19:18:32] npm ERR! cwd C:\projects\heartbeat\Heartbeat.Web
[19:18:32] npm ERR! node -v v0.10.32
[19:18:32] npm ERR! npm -v 1.4.28
[19:18:32] npm ERR! path C:\Users\appveyor\AppData\Roaming\npm-cache\695421b6-adable-stream-1-0-32-package-tgz.lock
[19:18:32] npm ERR! code EEXIST
[19:18:32] npm ERR! errno 47
[19:18:32] Command exited with code 47

It looks like it may be related to this npm issue: https://github.com/npm/npm/issues/6309

The command does work on my dev machine by the way. (npm version: 1.4.9)