I tried to fullfill the following challenge:
The following formula, meant to return the last day of the current month, has a couple of errors in it:

IF( MONTH( NOW() ) = 12,
  DATE( YEAR( NOW() ), 12, 31 ),
  DATE( YEAR( NOW() ), MONTH( NOW() ) + 1, 1) - 1

Create a new formula with the same label, name, and data type that successfully compiles.
- The formula should be of Date type and on the Case object
- The formula should have the name Last Day of Month and the resulting API name Last_Day_of_Month__c
- The formula should return the last day of the current month

I created a new formular field named "Last Date of Month" for the case object. My formular is as follows which has no syntax errors:
IF(MONTH(Today()) = 12,
  DATE(YEAR(Today()), 12, 31 ),
  DATE(YEAR(Today()), MONTH(Today()) + 1, 1) - 1
)

However, I got the following error message when I try to approve the challenge:

Challenge Not yet complete... here's what's wrong:
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, You can only set a case as escalated if it is high priority and not closed: [IsEscalated]

Has anyone a clue what I did wrong?

Many thanks in advance.

We are using a CTI tool called Avaya which is integrated with salesforce and users can call through a soft phone, they will have click to dial functionalities etc...

One of our user's machine freezes when he is in the middle of the call (thru soft phone) and he could not do anything for 5 mins. I guess it is some issue with Avaya softphone. Did anyone used Avaya before? Did anyone encounter this kind of issue?