iCal problem with Exchange 2007 on Mac Pro 3,1

I have the following products at home:

1. Early 2008 Mac Pro 3,1 Quad-Core Intel Xeon with OS 10.6.8.

2. iPhone 4, iOS 7.1.2

3. iPad, iOS 7.1.2

My workplace uses OWA for email, calendar and contacts.

On the iPhone and iPad, I am able to set up the OWA email and Calendar via Exchange 2007 so that they show up in my Apple mail and iCal and work perfectly.

However, while I have set up the OWA email using Exchange 2007 on my Mac Pro at home (which works just fine), I cannot add the OWA calendar to iCal using Exchange 2007. I can set everything up (add new iCal account; select "Automatic"; put in my work email address; and provide my username and password). The account name appears on the account names panel of my iCal window, but with the little "! within a triangle within a circle" icon. When I double click on this it then tells me the email address I have given is "not a valid email address."

When I contacted the IT, the tech guy said,

"I believe the problem is related to Apple Calendar being out of sync from the Exchange server. The first problem I’ve noticed is that [you are] using the Apple iCal for Exchange 2007, which is not valid since we are using Exchange 2010."

He suggested that I could try the solutions available at http://support.apple.com/kb/TS2481. I did this to no avail (syncing, deleting cache files, etc.).

He also said the solution might be for them (IT) to make a new Global Address List and update the GAL identity (I am paraphrasing since the email I got from him wasn't clear). I don't know if this has been done yet.

So my questions are:

1. Why is my iCal Exchange account working just fine on my iPhone and iPad but not on my Mac Pro?

2. Why am I getting a message that the email address I am using for my OWA account is not a valid email?

3. If there is a problem with my GAL identity, why doesn't it affect my iPhone and iPad?

4. Is there an Exchange 2010 for iCal? If so, how do I access it?

Any help greatly appreciated.