I can get some screens to work. Showing an object with day or month calendar works but when I switch to week view it crashes (more or less) with the error above. Same for the complete overview list where nothing shows up.

PHP 5.4.9
IIS8

Really hope this can be fixed soon because my clients are waiting.
Last time it took more than a month to get an answer......

I have exactly the same problems. I can view them when monthly calendar is choosed but not with weekly calendar.
Of sourse i can't use monthly calendar for all my objects as it is rental of a riding facility per hour or half day and also another object per hour based so I also really hope this will be solved soon.
Did you have the same problem after upgrading to the new version?
Artio team fixed it for me last time so I guess it can be done but it seem to be very low priority....

Well I am comfortable working in my PHP files and fixing things if needed but last time they did not tell here in the forum what was the fix. Nothing to re-apply now.

I came from a 1.4.x version that also took some time to get working....

Hello, problem with strftime('%W') on the IIS should be fixed in the latest 1.5.7.

Great! I can confirm everything works fine now.

Thanks a lot for this.

Perfect Jiri! Many thanks for this!
Have you considered the custom work yet?