installed my Win8 RP using USB as a second OS on my PC. The original OS is Win7, on volume C and the Win8 lies on volume D.
Now when I try to activate Win8, I get the following error:
Error Code:

0x8007007B
The filename, directory name, or volume label syntax is incorrect.
Is that because I installed my Win8 on volume D?

Step 1:
Perform the steps mentioned below and see if it helps.
1) Right Click at the bottom left of the screen and select System.
2) Click View Details in Windows Activation under Windows Activation
3) Click Activate.

Note: Make sure you are connected to the Internet when performing this step.

Step 2:
Perform the steps mentioned below and see if it helps.
1) Right Click at the bottom left of the screen and select Run.
2) Now type Slui 4 in the Run dialog box and hit enter.
3) Select the nearest location and click next.

You can try to activate by phone instead of over the internet.