The tag is present in Lintian version 2.104.244. That is the most recent version we know about.
The latest changelog entry has a version that matches one used in the specified previous entry. All versions of a source package must be unique even after a leading epoch has been stripped off.
Files generated by the current version of this source package would conflict with some historical files. This is because the Debian archive does not allow multiple files with the same name and different contents and the generated .dsc, .deb, etc. do not embed the epoch in their filenames.
Please pick another version, for example by increasing the Debian revision.