In some cases, the analysis shows which driver are causing the error. This Technet-thread contains parts of a setuperr.log with indications that something went wrong during WLAN driver init. Then it's possible to open the log-files in Windows editor. We need to copy the *.log files via context menu to the desktop. In folder Panther are *.log files, while folder Rollback contains *.txt files. Windows 10 setup creates log files located in the hidden folders: The error has been reported also during Upgrade to Windows 8.1 and indicates, that something went wrong exchanging/copying.

INSTALL_RECOVERY_ENVIRONMENT is the environment used by Windows 10, to process a rollback to the previous Windows install, if an non recoverable error occurs. The installation failed in SAFE_OS phase with an error during INSTALL_RECOVERY_ENVIRONMENT operation. The copy process stops at 84% and setup drops error code 0xC1900101 – 0x20004. This is the step, where install files are copied to the destination partition.

The users are observing that install progress stall at 25%. The error has been reported during upgrading Windows 7 or Windows 8.1 to Windows 10 (final and Preview Builds).