I have attached a fixed se/datetime/DateTime.e module that should fix this for all. Beta users can also use this file since it is exactly the same between versions.
0a. Temporarily move your system time forward in time by 1 day, or
0b. If you do not have permissions to change your system time, delete your state file in your config-dir, which may give you enough time to load the offending module before the error*
1a. Backup your existing macros/se/datetime/DateTime.e and replace with attached, or
1b. If you do not have permissions to replace the file, put the file in some location you do have write permissions (Desktop).
2. Load the new DateTime.e from Macro>Load Module, or
*Where is my config directory?
Windows default for v15.0.1: .../Documents/My SlickEdit Config/15.0.1/
UNIX default for v15.0.1: $HOME/.slickedit/15.0.1/
We will roll this into a hotfix ASAP. Thanks!