Errors encountered with different visualizations while using a Live Connection

Hi All!

I am using a live connection to a tabular model for my dashboard and I am facing a host of problems :

1. When I create a new Measure. For example: NewMeasure = Sales[Value] / Sales[Quantity]. All works perfectly.

    But when i try to use Sales[Value] or Sales[Quantity] in other visualization it returns me an error: "Unexpected exception"

2.  

   And when the measure is throwing an error, I  create a measure manually such as [salesvalue1] = Sales[Value], the created measure works but the inbuilt one doesn't. I usually get the error details as "Failed to execute DAX query" 
3. Many times, when I open my dashboard, a lot of visuals throw the error "Unexpected Exception" and when the same dashboard is opened in other systems, the visuals work fine. (Can this be related to memeory issues) 
4. When I am publishing the dashboard on the PowerBI portal, there is an immense lag and some of the visuals again throw the error "Unexpected Exception" even though the measures used for creating them are correct.

Any ideas regarding any of the problems?

Any sort of help is hugely appreciated.

Thanks in advance.