I am using PREVGROUPVAL to calculate YoY change by month (Sales in january 17' vs Sales in January 18).  It works fine, but it is assigning a value to February and March of 17' by comparing it to January and February of 18'.  It should leave these blank.  See attached image.  I need this comparison only to compare values within the parent group (Month in this case).  I have the report grouped as follows

Created Date: Month In Year
----Created Date: Year

Here is our setup:

We have actual sales data imported as a custom object as a child to the Account object.  Each month we use data loader to upload a new record with some apex that designated the newest batch file as "active" to ensure the proper numbers are bing referenced.  Some examples of fields from this object are "January CY Sales", "February CY Sales", etc.

I am wanting to create reports and charts that will show me January's prior year for all accounts for our sales members while referencing their current year's opportunity rollup for the same month to let them gauge accuracy on forecasting.  I have the objects related through a bridge custom object, but the problem is getting dates to line up.

I need a formula to calculate turnaround time based on the record's last modified date and it's created date.  I currently have last_modified_date-created_date, but I want to exclude weekends.  How do I modify formula?

I receive the following error when attempting to create new opportunities.  I can update existing ones just fine.  The apex trigger in mention hasn't been updated since 2013.

Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger Opportunity_UpdateNextTask caused an unexpected exception, contact your administrator: Opportunity_UpdateNextTask: execution of BeforeInsert caused by: System.NullPointerException: Attempt to de-reference a null object: Trigger.Opportunity_UpdateNextTask: line 25, column 1

Hello, I need to create a workflow rule that triggers when the opportunity stage changes and sends an email, as long as it doesn't change to some values, this is what I got that isn't working:
 

IF(
ISCHANGED(StageName) 
AND (
 NOT(ISPICKVAL(StageName, "Value 1")), 
 NOT(ISPICKVAL(StageName, "Value 2")),
 NOT(ISPICKVAL(StageName, "Value 3")),
 NOT(ISPICKVAL(StageName, "Value 4"))
))

 

I receive the following error when attempting to create new opportunities.  I can update existing ones just fine.  The apex trigger in mention hasn't been updated since 2013.

Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger Opportunity_UpdateNextTask caused an unexpected exception, contact your administrator: Opportunity_UpdateNextTask: execution of BeforeInsert caused by: System.NullPointerException: Attempt to de-reference a null object: Trigger.Opportunity_UpdateNextTask: line 25, column 1