令人困惑的编译错误

Question

fontspec-xetex.sty 1767
Forbidden control sequence found while scanning use of \__cs_generate_from_si
gnature:nnNNNn.
<inserted text> 
                \par 
l.1767       \int_case:nnn

有什么问题？这个文件有什么变化吗？

在控制台输出窗口中，错误如下：

Runaway argument?
{\dim_set:Nn ##1{\fontdimen ##2##3}\dim_compare:nNnT ##1={0pt}{\settoheight \ET
C.
! Forbidden control sequence found while scanning use of \__cs_generate_from_si
gnature:nnNNNn.
<inserted text> 
                \par 
l.1767       \int_case:nnn
                           #2
? 
`