Thanks. None of this applies since it assumes adblock is installed. My problem is that the installation halts because it is looking for an msi with a different name which doesn't exist. I have just tried again (without add-ons) and checked the source C:\Users\<me>\AppData\Local\Temp\is-9CDS2.tmp given by the error box and it isn't there. There are however two files called is-8779K.tmp and is-T3QMP.tmp so something is going wrong somewhere. I assume one is for 32 bit and the other is for 64 bit so it would be unwise to modify the source requested without knowing which. Both have the installation timestamp. When I exit the Windows Installer error message, these tmp files disappear. If it helps I am using 11.0.48 with Windows 10 Home 32 bit build 16299.rs3_release. 170928-1534. Adblock was installed previously but had to be removed to fix another problem with a conflict affecting IE due to recent updates. Discussions with an elevated Microsoft troubleshooter yesterday suggested that AppData is not a safe place to put things anymore.