I don't know the details of this particular recipe, so you'll have to excuse me if this comes across as a bit of a shot in the dark, but here are a few things that could have gone wrong:
Grainy chocolate is usually a sign of seizing. White chocolate still contains cocoa butter and can still seize. Therefore it's important not to let any liquid touch the melting chocolate and to not let the temperature get too high.
130-140° F is definitely way too high. White chocolate will normally burn or seize at temperatures higher than around 110° F. You mentioned that the second time you used the right temperature, but it's worth pointing out anyway: Be very careful with the temperature, don't use direct heat preferably, use a double boiler or a stainless steel bowl placed over a steaming pot, and stir frequently to keep the temperature even.
Don't dump hot cream into the chocolate. It's strange that almost every recipe tells you to do this; water causes melted chocolate to seize, period. The only way to avoid this is to use a very large amount of liquid for a very small amount of chocolate, so what you have to do is go the other way; incorporate the chocolate into the cream, a small amount at a time. This is especially important with tempered chocolate because you've essentially raised the melting point!
Also be careful not to let any water get into the chocolate as it's melting; use dry utensils and make sure you don't have any steam condensing over top (use a large bowl over a small pot if you don't have a double boiler).
Finally, as Joe commented, make sure you're using the right kind of white chocolate. I've never seen baker's white chocolate, so when I need white chocolate for melting I generally use the white chocolate chips. If yours didn't burn at temperatures as high as 130° F then you might have been using coating chocolate instead.
Follow all those precautions and you should end up with a very smooth mixture. I've done this for ganaches and even foams and it's never a problem if you're careful about both the temperature and moisture.
Disclaimer: I've never tried to make a ganache with olive oil, so take that into consideration as you read the following.
First, I have to assume that you're trying to use olive oil to replace the cream that's normally used in making ganache, perhaps to make a non-dairy ganache. If that's not right, please clarify your question.
Ganache is essentially an emulsion of cocoa butter (usually from chocolate) and cream, plus vanilla and/or other flavorings, that is allowed to cool to the point where the cocoa butter solidifies. It's the solidified cocoa butter that gives ganache it's firm texture. The greater the ratio of cocoa butter to cream, the firmer the ganache will be. If you want to replace the cream, you'll need to make sure that you replace all the components that have an effect on the emulsion. Harold McGee's On Food and Cooking explains the structure of ganache:
The continuous phase of this mixture, the portion that permeates it,
is a syrup made from the cream's water and the chocolate's sugar.
Suspended in the syrup are the milk fat globules from the cream, and
cocoa butter droplets and solid cocoa particles from the chocolate.
He doesn't say it, but I'd guess that the milk proteins from the cream might act as emulsifiers to help stabilize the emulsion, much as they do with butter.
The melting point of olive oil is obviously different from that of butterfat, but since you heat the cream in order to make ganache anyway, olive oil might still work. Given what McGee says, you'll need to make sure that you add an appropriate amount of water so that there's enough syrup to suspend the butterfat, cocoa butter, and solids. How much is an appropriate amount? Cream is usually 20-40% butterfat, so starting with a 1 part oil for 2 parts water seems reasonable. You might also need to add something that'll act as an emulsifier, like lecithin.
Best Answer
Ganache is a mixture of cream and chocolate, made by heating the cream and mixing in the chocolate until smooth and fully incorporated. Butter is then often added to give the final product a characteristic "shine". Ganache can be used as a filling or as a coating/topping in truffles and is a frequent component in other desserts.
I've encountered "chocopaste" at an Indian grocer before, and it is essentially a homogenized mixture of chocolate and milk with other ingredients. It has a similarity to ganache in that it contains chocolate and dairy combined. The commercial chocopaste I've seen have also had other ingredients (added fats and/or sugars, stabilizers, preservatives, etc.), unlike ganache made at home which would contain only cream and chocolate. In this way chocopaste is somewhat like Nutella, the chocolate-hazelnut spread. In fact, the chocopastes I've seen came in similarly-shaped jars.
Chocopaste appears to be used as everything from a dessert topping or filling to a base for making chocolate drinks.
Here is an example of chocopaste, containing the following ingredients:
In terms of substituting one for the other, the added stabilizers, sugars, and flavors in chocopaste may affect the final product. Hydrogenated vegetable fat isn't the same as butter either, so mouthfeel and flavor will not be the same.
I would expect different chocopastes to potentially vary in terms of flavor and sweetness. For uses as filling/topping/etc, I would just try out whatever products interest you and compare for yourself.