>macs_peak <- system.file("extdata", 'H820_OsiR_1_peaks.xls', package = "ChIPpeakAnno")`
> macs_peak

[1] ""

> macs_peak_gr <- toGRanges(macs_peak, format = "MACS")
Error in read.table(data, header = header, comment.char = comment.char,  :

system.file can not work

ChIPpeakAnno stores several example files under its extdata directory for demonstration purposes. These files can be found with the system.file() function. That being said, if the file (e.g. "H820_OsiR_1_peaks.xls") is not pre-existing in the package, system.file() will not find it. A side note, you have an extra backtick ("`") at the end of your first commend.

Ensure that the file path is correct abgerny and that R has permission to access it. If you're working with a file located on a network or external drive, try moving it to a local directory to eliminate potential path or access issues.