Pages rapidly dropping out of Google

My forum is 8 years old, previously it was on phpbb and I switched to Vbulletin + VbSeo last December.

I have noticed that the number of pages indexed in Google has been dropping steadily for quite some time. I'm now down to just 2,310 pages in Google and dropping further every few days (using a site: search) yet my forum has 17,000+ threads. In Yahoo I have 36,000+ pages indexed and 16,400 in Bing.

While my traffic is definitely up since my switch to vbull+vbseo and I'm pulling in a host of long tail searches I never previously had, the ever reducing number of pages indexed has me a little concerned.

Is there anything obvious I'm doing or not doing that could be the cause of this?

Is there anything I can do to get my pages crawled more deeply?

Is there anything else I can do to improve the on page SEO of my forum?

Also could someone tell me what the archive is all about:
http://www.cancuncare.com/forum/arch...p/f-9-p-3.html
Is this a good or bad thing to have? Traffic to the archive accounts for just 0.04% of overall traffic.

My forum url is:
Cancun Forum and Temptation Cancun Message Board

Ok, done a little reading around. I've disabled the archive and installed the VBseo sitemap generator, lets see if this makes a difference.

Hello,

Yes, we generally recommend the archive be disabled unless it is a significant traffic source already from being a legacy application. A drop in total urls is expected, as vbseo cleans up all of the duplicate urls you had previously. Did you use our 404/301 tool when migrating? any old phpbb traffic/links may all be getting lost without it. This should be left in place indefinitely.
404 / 301 Tool After Import Redirect on ImpEx imported forums - vBulletin SEO Forums

Yes I used the 404/301 redirects and all my old phpbb urls have been redirecting fine since I switched 9 or so months ago. I did have a ton of pages in there but it's only the last couple of months that they have started dropping out.

I've, today, disabled the archive also installed the site map generator and fixed some canonical issues.

I hope that leads to increased indexing. Is there anything there on my forum you see I should change? I did post in the critique forum several days ago but no reply as yet.

Hello Stephen,

I just checked your sitemaps and it seems you have installed vBSEO Sitemap Generator 2.5 with vBSEO 3.5.2, so that all of your URLs inside sitemaps are wrong. Please try to upgrade to vBSEO Sitemap Generator 2.6 to fix that issue.

I also replied to your critique thread, please check out and let me know if you have any further question:

Critique please

Best regards.