# After update TL 2015 to 2017 bibliography doesn't work anymore

I juste update install TexLive 2017 on my windows system today (I was using TL 2015 until now). I am using (last version `2.12.8`) texstudio as an editor.

My MWE is working well when I open an new document. However when I try to compile documents created with TL 2015, I have many errors.

I cn't understand why things seem to work with the new document while getting so messy with the previous documents.

The `log file` indicate many `! Undefined control sequence.`

I also get a file called: `myfile.bbl` which indicate the following things that I don't understand:

``````% \$ biblatex auxiliary file \$
% \$ biblatex bbl format version 2.5 \$
% Do not modify the above lines!
%
% This is an auxiliary file used by the 'biblatex' package.
% This file may safely be deleted. It will be recreated by
% biber as required.
%
\begingroup
\makeatletter
\@ifundefined{ver@biblatex.sty}
{\@latex@error
{Missing 'biblatex' package}
{The bibliography requires the 'biblatex' package.}
\aftergroup\endinput}
{}
\endgroup
``````
• Did you remove the temporary files before you compiled with the new version? The `.bbl`, `.bcf` and `.aux` files were written by an older version of the package and can cause problems. If you delete them and recompile things should work. – moewe Apr 12 '18 at 13:28
• Somewhat related tex.stackexchange.com/q/410512/35864 – moewe Apr 12 '18 at 13:46
• If we are talking about the temporary file to be find here `C:\Users\myself\AppData\Local\Temp\etc...`, yes I did delete it (several times) without success with compilation. – mailysmanu Apr 12 '18 at 13:57
• ok I understand your point and it seems to be working – mailysmanu Apr 12 '18 at 14:01
• Mhh, actually I was talking about the `.bbl`, `.bcf`, `.aux` files in the same directory as your `.tex` file with the same basename as your `.tex` file. Like the `myfile.bbl` you show us. These temporary files are created by TeX to 'remember' certain things between compilations or to communicate between Biber and `biblatex`. If you compile a document that was previously compiled with an older version of `biblatex` there will be a version mismatch.- – moewe Apr 12 '18 at 14:01

Delete the temporary `.aux`, `.bbl` and `.bcf` files. Then recompile from scratch with the full LaTeX-Biber-LaTeX-LaTeX sequence.
These temporary files are used to communicate between `biblatex` and Biber or to remember things between LaTeX runs. They often contain internal macros whose structure may change between `biblatex` versions. See Matching biblatex in two machines. Since the temporary files are automatically re-created if you do a full LaTeX-Biber-LaTeX-LaTeX run, it is safe to delete them and then just do a full compilation run.