Damon Dash Jay-Z's Ex-Biz Partner ROC-A-TAX LIEN

7/7/2013 9:10 AM PDT

Damon Dash -- Jay-Z's Ex-Biz Partner ... ROC-A-TAX LIEN

Damon Dash probably wishes he still had Jay-Z on speed dial ... because the cesspool of debt he's wading in just got worse ... he's been slapped with a $2.8 MILLION TAX BILL.

Dash -- who co-founded Roc-A-Fella Records and Rocawear with Jay -- has been open about the fact that he's drowning in debt ... despite the fact that at one time he was half-king of a multi-million-dollar business.

Now, his financial problems have worsened. Uncle Sam filed a federal tax lien against Dash, claiming he needs to cough up some un-paid tax cash for the years 2005 and 2011. The breakdown:

2005: $2,614,918.10
2011: $187,544.20

Grand total: $2,802,262.30 ... i.e. a whole lotta cheddar.

The 2005 bill is clearly larger ... which makes sense considering Hov and Dash parted ways back in 2004 -- meaning in 2005, he was probably still raking in some major-taxable bucks. 2011 ... not so much.

FYI -- Dash has said he owes millions in back taxes to the State of NY and NJ and claims he's lost multiple properties to foreclosure.

Meanwhile, Jay ... is still super rich.