尝试安装 placeins，但是不起作用。
\documentclass{article}
\usepackage{placeins}
\begin{document}
Text
\end{document}
在 TeXstudio 的日志中，它显示
Process started: pdflatex.exe -synctex=1 -interaction=nonstopmode "test".tex
Unfortunately, the package placeins could not be installed. Please check the log file: C:\Users\cr\AppData\Local\MiKTeX\2.9\miktex\log\pdflatex.log
在指定的文件中，它读取
2019-11-13 11:26:42,373+0100 INFO pdflatex - starting with command line: pdflatex.exe -synctex=1 -interaction=nonstopmode test.tex
2019-11-13 11:26:42,380+0100 INFO pdflatex - allowing known shell commands
2019-11-13 11:26:42,381+0100 INFO pdflatex - enabling input (output) from (to) processes
2019-11-13 11:26:42,513+0100 INFO pdflatex - installing package placeins triggered by tex/latex/placeins\placeins.sty
2019-11-13 11:26:45,304+0100 INFO pdflatex - mpm: starting package maintenance...
2019-11-13 11:26:45,306+0100 INFO pdflatex - mpm: installation directory: "C:\Program Files\MiKTeX 2.9"
2019-11-13 11:26:45,306+0100 INFO pdflatex - mpm: package repository: http://ftp.rrze.uni-erlangen.de/ctan/systems/win32/miktex/tm/packages/
2019-11-13 11:26:45,663+0100 INFO pdflatex - mpm: package repository digest: 6f45c497f2c9e9dd7da60de60809775d
2019-11-13 11:26:45,691+0100 FATAL pdflatex - The requested package is unknown.
2019-11-13 11:26:45,691+0100 FATAL pdflatex - Info: ="name="placeins""
2019-11-13 11:26:45,691+0100 FATAL pdflatex - Source: Libraries\MiKTeX\PackageManager\PackageDataStore.cpp
2019-11-13 11:26:45,691+0100 FATAL pdflatex - Line: 394
2019-11-13 11:26:45,845+0100 INFO pdflatex - finishing with exit code 1
编辑：
当我尝试手动打开 MiKTeX 控制台时，屏幕右下角出现了这条小消息：
如何解决此问题？