This issue is fixed in a site cumulative update.
9.2 SP2 CU19, 9.1 SP3 CU44, 9.0 SP3 CU30
- EKTR-466: Increase permissiveness of loading known XSLT files
Apply the latest CU to resolve this issue.
Downloads and Install Instructions
As a workaround, add the following file to the XSLT whitelist. Any other custom XSLTs should be whitelisted as well.
C:\inetpub\stage\WorkArea\calendarAdmin\xslt\calendaradmin_dtselectordatetime.xsl
How to add acceptable XSLT files to the system
Add the following line to the whitelist file.
<xslt>calendarAdmin\xslt\calendaradmin_dtselectordatetime.xsl</xslt>