Change your char() to varchar(), or trim the variables. You are trying to concatenate 2 50 character fields into 1 50 character field. They do concatenate, but with 33 space characters in between, and are then truncated to first 50 characters.
So either:
Declare @path varchar(50), @path1 varchar(50)
Declare @file varchar(50)
select @path = '\\server\server1\'
select @file = 'file.txt'
select @path1 = @path+@file
Or:
select @path1 = RTRIM(@path)+ RTRIM(@file)
Hope this helps