Found the problem.

For Subsilver2 Style

File: styles/subsilver2/template/portal/block/mini_calendar.html

Find:
<td class="row1" align="center"><span class="gensmall">{mini_cal_row.mini_cal_days.MINI_CAL_DAY}</span></td>

Replace With:
<td align="center"><span class="gensmall">{mini_cal_row.mini ...

Actually, I am beginning to think this is an error within Portal3 - Calendar, and not an installation error on my part.
Here is another board that I found that is using a subsilver2 based style with the calendar active.

http://kotrwrath.shadowroute.net/

When viewed in Internet explorer, his site ...

Your Portal Version: 1.0.3
Your phpBB Type: Standard phpBB3 (v. 3.0.5)
MODs installed: Yes - User Blog Mod, Instant Redirection (for posts and log in only), Apache mod rewrite SSL for log in and adm functions
Your knowledge: Basic Knowledge

What have you already tryed to solve the problem ...