Emergency for background check!!!

Laotu and every Daxia,

A background check company is doing background check for a employer who wants to hire me. They are asking W2 from a particular compamy on my resume. I don't have W2 from this company(it's my friend's business. I did some projects for them. But I list it as a full time contractor in my resume-over one year. My friend wrote a letter to verify the employment and pay rate in his company, but they keep asking the W2). I know I am in the bad position. How can I explain this to make up? Or I have to withdraw the offer?

Any recommendations are welcome!!!