Does a High Yield Dividend stock such as 45% mean that it is not worth buying?
No - it just means that its recent dividends were 45% of its current price. It could mean that the price has tanked recently, inflating the average. If it paid out 4.5% previously but the stock is now worth 10% of its value at the time of the dividend, then its current dividend rate would be 45%. Whether it will continue to pay dividends at that rate, or whether its share price will go up (reducing the yield) is not known, so there's no way to say for certain if it's worth buying or not.
How could a company have such a high dividend yield rate?
Most likely it's because the share price has dropped dramatically, inflating the dividend rate. I don't know of any company that has enough spare cash to pay out half of its value in dividends.