Norwegian keyboard keys don't work with Ubuntu in VirtualBox

I just installed VirtualBox (from Oracle) in Windows 7, and created a virtual machine with latest Ubuntu.

Here in Firefox I can use the left Ctrl key, while the right one doesn't have any effect. However, I can't use the AltGr key (also known as Right Alt) to produce e.g. curly braces like {} (I pasted that via Ctrl V).

In a terminal window I can switch the "Input method" to "Multipress", and then I can use AltGr to type e.g. {}, which is how I produced those characters for this posting. However, with "Multipress" the Ctrl keys seem to have no effect whatsoever. So in order to e.g. type Ctrl D I have to right click and switch the "Input method" to "System (IBus (Intelligent Input Bus))". Then AltGr does not work. So that intelligent input method is apparently not particularly intelligent. Even the acronym fails to make sense.

I tried specifying the compose key in the system settings keyboard layout.

With that, neither Ctrl nor AltGr worked.

Here's what xmodmap reports:

[~]
$ xmodmap -pke | grep -i control
keycode  37 = Control_L NoSymbol Control_L
keycode 105 = Control_R NoSymbol Control_R
[~]
$ xmodmap -pke | grep -i alt

keycode  64 = Alt_L Meta_L Alt_L Meta_L
keycode 204 = NoSymbol Alt_L NoSymbol Alt_L
[~]
$ _

How can I fix this?

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Edit: additional info: the keyboard is a standard PC keyboard, a Logitech K120, with Norwegian layout.

Answer

I got the AltGr key working in Ubuntu. I just had to know that I should create a file called ".Xmodmap" and add this line: "keycode 113 = Mode_switch Multi_key". Which I found in a bug report about a similar issue, at https://bugs.launchpad.net/ubuntu/+source/xkeyboard-config/+bug/349487/comments/1