R project "unexpected string constant" error when program start

When I turn on my R project, this strange error occurred.

Error: 1:41: unexpected string constant
4: 
5:         if(capabilities("
                                           ^

I reinstalled it twice, but the same problem happened. The same problem occurred when installing the lower-version(3.3.1).

Due to this error, I can not make any R markdown document.

This is my session information.

sessionInfo()
R version 3.6.2 (2019-12-12)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Mojave 10.14.5

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] compiler_3.6.2 tools_3.6.2   

I'm really want to know how to deal with this strange error. Thank you!