Hi,
thanks for the information. I do not know how it was created as it comes as part of the opensource monitoring project checkmk. With your information I was able to repack it using the following commands
fakeroot sh -c '
mkdir tmp
dpkg-deb -R file.deb tmp
dpkg-deb -b tmp file-new.deb
'
Afterwards I was able to upload it.
Nevertheless you might want to consider allowing trailing slashes in a future release as the link you provided states they are allowed:
...Only the common ar archive format is supported, with no long file name extensions, but with file names containing an optional trailing slash, which limits their length to 15 characters (from the 16 allowed)....