一個混亂的編譯錯誤

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

它出什麼問題了 ？這個文件有什麼變化嗎？

在控制台輸出視窗中，錯誤如下：

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
? 
`