Hmm..

Well, has this happened to anyone:

Since I have a job now and I have a steady income, I decided to put my 3 years of anticipation to rest and have my mom purchase NL. Well, low and behold, we get to the last step of the verifaction and then it says something like "Credit card no valid" or something on that lines.

Has anytone had that problem and know a good solution?

Get your mom to call her credit card company and make sure she is allowed to make online purchases and that her account is fine.
If it still gives you that message, try contacting the NL people or MadData (I'm not sure which one deals with the payments or if MadData just serves as a distributer...).