Error "problem unlinking" in apt-get clean

There's a problem whenever I try to use sudo apt-get clean:

:~$ sudo apt-get clean
W: Problem unlinking the file apt-fast - Clean (21: Is a directory)
:~$ apt-fast clean
W: Problem unlinking the file apt-fast - Clean (21: Is a directory)

Purging apt-fast and running sudo apt-get clean is the only way I found that fixes this problem.
But I use apt-fast a lot, so not using it is not a good solution.
Reinstalling apt-fast and running sudo apt-get clean makes the problem pop out again.

Additionally, while installing (I don't know whether this will be useful), I found this problem:

Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/\${ <-- HERE _MAXNUM}/ at /tmp/apt-fast.config.NDgAmi line 205.
Selecting previously unselected package apt-fast.
(Reading database ... 498722 files and directories currently installed.)
Preparing to unpack .../apt-fast_1.8.3~137+git7b72bb7-0ubuntu1~ppa3~wily1_all.deb ...
Unpacking apt-fast (1.8.3~137+git7b72bb7-0ubuntu1~ppa3~wily1) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up apt-fast (1.8.3~137+git7b72bb7-0ubuntu1~ppa3~wily1) ...
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/\${ <-- HERE _MAXNUM}/ at /var/lib/dpkg/info/apt-fast.config line 205.

Also I am using Ubuntu MATE 16.04.

Thanks.

Solution 1:

A potential solution is to remove the directory /var/cache/apt/archives/apt-fast every time you want to run apt-get clean.

$ rm -r /var/cache/apt/archives/apt-fast

This also means you are clearing the cache for apt-fast.

Solution 2:

To prevent display this error, you can remove "/var/cache/apt/archives/apt-fast/" directory and change the DLDIR variable in /etc/apt-fast.conf to another path (i.e. /var/cache/my_apt-fast/archives/apt-fast).