Why was Swiss National Bank in red by keeping fix exchange rate to Euro? When I read news about the action of Swiss National bank of not keeping fix ration to Euro any more, I read in all articles, that it was too expensive for Swiss National Bank to keep the fixed exchange rate. I don't really understand how can it be expensive. Swiss N.B was printing Swiss Franc and selling it for Euro? Right? How can be expensive printing and having Euro for free?
From a central bank's point of view, printing money isn't free.  Each 1 CHF created costs exactly 1 CHF - that is, it appears on the bank's balance sheet as a liability.  They owe that 1 CHF to someone (the person they bought the Euros off - a bank).  And whenever you owe someone money, there is always the ultimate belief that you can pay it back.  Lose that and the bank fails, and the currency fails.

With central banks this isn't clear cut, since the money can only be "paid back" by destroying it, but the trust in fiat money relies on the solvency of the central bank.  A sort of, "so long as you could pay it back, I'll never ask you to".

The SNB had been buying so many Euros (and other currencies) that it was sitting on foreign reserves worth about 85% of Swiss GDP.  In the process it did make a lot of profit, but that can only go on so long.

In theory, if the SNB could have held out forever, then it could have beaten the ECB, and when the Euro eventually strengthened, unwound its position as a profit.  But that would have involved the SNB conducting massive quantitative easing in the mean time, in order to supply the world with sufficient CHF to meet demand.  Given that Switzerland is somewhat smaller than the Eurozone, it would have been a battle it was destined to lose.

Given that they knew they would likely lose eventually, it is better to lose now, when you only have 85% of GDP in Euros, than to lose later on when you have 850% of GDP in Euros!

Of course having a central bank that is completely screwed, would weaken the CHF, but they only want moderate weakness, no complete destruction of the currency!