My understanding is that because this symbol has been introduced only 5 years ago, many computers don’t contain it yet. Especially older computers.
Out of curiosity, what’s your operating system?
Here is some relevant information from Wikipedia:
Ubuntu became the first operating system to support the Indian rupee symbol by default. Since its 10.10 version it has supported the symbol out of the box, as it was added to the Ubuntu font family by a contributor. Since then, it has been included in various GNU/Linux distributions.
On 18 May 2011, Microsoft released an update KB2496898 to Windows Vista, Windows Server 2008, Windows 7 and Windows Server 2008 R2 operating systems to include support for this new Indian rupee symbol. With the Windows update, it is now possible to use alt code text entry to obtain the Indian Rupee symbol – Alt 8377. On systems running Windows 8, the symbol can be typed using the English (India) keyboard layout with the key combination Alt Gr+4.
Apple Inc. has added support for the rupee symbol with iOS 7. Mac OS X Lion (10.7) also includes the new Indian rupee symbol and can be found in the Character Viewer. As of Mac OS X Mountain Lion (10.8), users using the Devanagari keyboard can enter the new Indian rupee symbol by typing Option/Alt+4 (a combination that yields the Cent symbol on a US keyboard layout).