What happened

Last week was a rough week for investors in 3D printer maker 3D Systems (NYSE:DDD) -- and this week isn't starting off much better. 3D Systems' stock fell 10% in early Monday trading after it was reported that analysts at Zacks Equity Research had added the stock to their "strong sell" list.

A 3-D printer

Image source: Getty Images.

So what

Zacks didn't provide a whole lot of context for its decision to downgrade 3D, saying only that the "Zacks Consensus Estimate" for 3D's current year earnings "has been revised 93.2% downward over the last 30 days." Be that as it may, analysts surveyed by Yahoo! Finance  are still predicting that 3D will earn about $0.44 per diluted share this year and grow that figure 27% to $0.56 per diluted share in 2018.

That said, Zacks' rating comes as just the latest in a series of Wall Street downgrades and price target cuts following last week's disappointing earnings release at 3D.

Now what

Admittedly, Wall Street stock ratings and downgrades don't always make a whole lot of sense -- but in the case of 3D Systems, I kind of think they do. You see, while consensus estimates may be calling for 3D to earn a "profit" this year, the profit they're expecting is only of the "pro forma" variety.

In contrast, when calculated under generally accepted accounting principles (GAAP), 3D Systems is not remotely profitable today. What's more, according to data from S&P Global Market Intelligence, Wall Street analysts who follow 3D Systems don't expect to see the company turn in actual GAAP profit before 2020 at the earliest.

Meanwhile, 3D Systems itself announced that it has decided to "withdraw" its own guidance on future profits, throwing investors into confusion over its prospects at the worst possible time. No wonder investors are still streaming toward the exits.