Error in UI-path when upgrading from EPiServer 5 to 6

The other day we were upgrading a site for a customer from EPiServer 5 to EPiServer 6. In the upgrade process an exception was thrown telling us:

At C:\Program Files (x86)\EPiServer\CMS\6.0.530.0\Upgrade\System Scripts\Upgrade Site (SqlServer).ps1:361 char:29

+                  $newUiUrl = $uiUrl.Replace <<<< ($uiPath, $uiPath+”/CMS”)

System.Management.Automation.ParentContainsErrorRecordException: Cannot convert argument “1”, with value: “/CMS”, for “Replace” to type “System.Char”: “Cannot convert value “/CMS” to type “System.Char”. Error: “Strängen måste vara exakt ett tecken lång.””

After some research we realized that the uiUrl in episerver.config was set to and the upgrade script didn’t like it and most likely expected the value to be ~/ui/.

The solution was to change it to ~/ui/ during upgrade and then change it back.