When upgrading a Sitecore instance where Active Commerce is already installed, you may receive this error when attempting to update:
System.IO.InvalidDataException: The magic number in GZip header is not correct. Make sure you are passing in a GZip stream.
This has been witnessed when updating from Sitecore 7.1 to 7.1 Update 2.
Cassette, a minification and bundling tool, appears to be interfering with the update.
Add the following configuration to your web.config file:
<configuration> <configSections> .... <section name="cassette" type="Cassette.CassetteConfigurationSection, Cassette" /> </configSections> <cassette rewriteHtml="false" />
Remove this configuration after the Sitecore upgrade is complete.