Sharing failed: Syntax error: Unexpected end of input

When I'm trying to give "test2 Visitors" access to test1 site I get the fallowing error "Sharing failed: Syntax error: Unexpected end of input" 

"test1 Visitors" is a Unique SharePoint permission group created when creating test1 site

"test2 Visitors" is a Unique SharePoint permission group created when creating test2 site

test1 site and test2 site are on the same site collection. 

tested with different sites and groups and the result is the same. 

tested with IE11 and Chrome to eliminate browser problem. 

Any idea what is the problem?

Thanks, Nir