The next issues may be occur during ARC Welder installation:
Unable to install extension on Google Chrome.
Message about non compatible app.
You use Google Chrome version lower then 40.
Upgrade Google Chrome and try to install ARC Welder again.
ARC Welder size does not match the app declared size.
ARC Welder takes a long time to load.
ARC Welder works in a bundle with such developer tool as App Runtime for Chrome. App Runtime for Chrome can be downloaded and installed together with ARC Welder. This increases installation package size up to 350 Mb.
If you have not installed App Runtime for Chrome on your Google Chrome yet, turn on developer mode in Google Chrome extension settings and wait until the both extensions will be installed.
After troubleshooting you can proceed installation.