Hiya,
The 1800-F has been discontinued by Denon, which I think says it all.
The 1800F was a bit of an embarrassing "Younger Brother" with regard to Denon's product range, hence why it was quickly followed with three additional models. The problem with new designs is that they are flawed, and customers who snapped up the first 1800's were in fact guinea pigs for Denon's designers

When a company launches a new product range, it is best to wait at least 12 months whilst the first models have all of their teething problems addressed, this way you are not likely to be plagued with firmware upgrades and product recalls
Unfortunately, the 1800 and Denon never fully recovered from the embarassment of the 1800F, which is why the 2100F and the 2600F models quickly followed, all slightly better products. The 1800F remained their "Budget" model.
Yes, the 1800F does have frequent errors when reading CDR's (Since the unit was originally designed before the widespread use of CDR's!). Other than that, the 1800F isn't a bad unit, and you may be lucky and have the latest version which is a little more stable.