Exact same error/dialog here following an upgrade to El Capitan 10.11 from Yosemite 10.10.5 on an iMac.
- Replaced /System/Library/Frameworks/CoreTelephony.framework from the El Capitan installer
- Deleted/reset all the iMessage DB/files/plists (I had no problems with iMessage, it was already and is still working fine under El Capitan)
- Same error occurs under a new test user-account (makes it look like a system-config/corruption/bug problem)
No issues with iCloud, iMessage, connecting to CIFS network shares, etc. Dialog pops up after user login, hangs around waiting for me to click "OK", and if ignored, it'll go away on its own after a few mins.
Of interest in my config, I have two drive, one SSD and one HDD. The iMac boots from SSD, but the actual "Home Directory" (/User) has been relocated to the HDD with a link pointing to the new location. Perhaps the 0755 error indicates that the new/beta CoreTelephony.framework cannot directly write to the filesystem linked "/User" folder as the actual/real HFS+ FS path is "/Volumes/DataDrive/Users/" (eg: a hardcoded FS write attempt to the /User path)? If this is the case, perhaps this is simply a minor bug that can be easily addressed in an update... If not, it must be a specific/unique mis-configuration issue.
Any ideas/trouble-shooting welcome! No joy from the folks at Apple (iMac is out of support window).