[R] package "methods" in options("defaultPackages") was not found

[D. Alain]

Dear R-List, 

I receive a strange error message when starting R. It says: 

"Warning message:
package "methods" in options("defaultPackages") was not found 
Error in file(filename, "r") : cannot open the connection
In addition: Warning message:
In file(filename, "r") :
  cannot open file 'G:/statpack/R-31~1.2/library/methods/R/methods': Invalid argument
Error : kann R Programmkode in Paket ‘methods’ nicht laden
During startup - Warning message:
package ‘methods’ in options("defaultPackages") was not found"

As far as I can see the package "methods" seems to be installed in my library.

When I load data I get 

simpleError in doTryCatch(return(expr), name, parentenv, handler): could not find function "is"

Can anyone help?

Thank you very much in advance.

Best regards

Alain

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