Could just be the paper you're using.
I tried recently a board printed at the warehouse, on their slightly shiny paper (200gsm) and while it transferred surprisingly nicely (I thought it would just stay on the paper) there were quite a few holes where paper fibers were stuck in the toner and seemed to pull it off.
I haven't noticed that problem with old magazine pages, which are noticeably more shiny and much thinner.
I would try repeating the process with something known to work well, preferably something designed for it like Pulsar Pro even. If you get problems even with that you know it's something else.
(But even they admit you can get pinholes\pitting with that, which is why they also sell the green TRF, although I don't think I've ever seen anyone who said they had needed to use that as well)
--- In Homebrew_PCBs@yahoogroups.com, DaveC <davec2468@...> wrote:
> I'm using a Brother HL-5170DN to print to thin glossy (not photo) paper.
>
> The printing goes just fine, as does the toner on the copper.
>
> But after etch, it looks like there were some pinholes in the toner:
> there are places in the copper where the copper is etched through in
> a point or right across a trace. If I were to tin the copper it would
> probably be OK to use.
>
> What is the cause? The toner adheres just fine to both the paper and,
> apparently, the copper.
>
> Suggestions?
>
> Thanks,
> Dave
>