Hi Thomas,
Did you upgrade the CTS Manager recently, and if so what version did you upgrade from?
This issue used to be fairly common with systems running versions prior to 1.7.2 (see CSCtj95619 for more details), and indicates that the CTS Manager is unable to find a timezone mapping between what is returned from the calendar server and what is in the local CTS Manager database. If CTS Manager is unable to resolve this mapping, then it resorts to scheduling the meeting without any DST offsets.
If your system was running a version prior to 1.7.2, and the affected meetings were booked prior to the upgrade, then the only workaround is to reaccept the meeting in outlook or OWA.
If the system was not running a version prior to 1.7.2, then can you please look in the CTS Manager GUI and click on Troubleshoot > System Messages, and search for any messages with the text "Unresolved timezone mapping" and copy the exact message?
Thank you,
Paul