A couple places to start:

1. Any direct General Journal or other journal postings to the inventory account?
2. Check Trial Balance against Stock Status report - do they match?
3. Check product line maintenance in IM Setup - anything other than "Inventory" posting to the inventory account?  Any product line posting to a different inventory account?
4. Any unposted entries? (Run Daily Transaction Register from General Ledger)
5. Any negative tiers? (not sure on this one but it doesn't hurt to ask).

Well if you have transactions dated in December 2015 I would say that is your issue. You need to work with your reseller and take a look at these transactions. Reverse them and get them in the proper month and year.

This is the Knowledgebase article that we recommend in Customer Support:

Inventory Reports do not match and do not reconcile to Inventory account in General Ledger

Please note that the Trial Balance DOES NOT use future dated transactions and if you have December 2015 transactions then there is no way it ties.

Link doesn't work.  :(

Correct BigLouie.  We will most likely have to go backwards, doing 0.00 entries to physical counts, and work backwards, then reenter a "physical Inventory Count" for the correct item counts, as they are correct now.  Ugh.

Luann - login to the support poral (support.na.sage.com) and the link will work :)

I should mention-I used to be a reseller.  We have already exhausted all the standard reasons why this may occur.  We know there were entries made into future fiscal years.  When we converted from 4.3 to 4.5 in October of 2013, bringing IM into the 4.0 arena out of legacy, there were fiscal years in the pat and future, as there were transactions with those dates.  The Sage tech we worked with on this must have missed the impact on some of the files in IM...  Now to fix, it appears we have to do physical count entries in the months where the errors are, zeroing out the inventory, and that may fix it.  Any other ideas?  I should have been more specific when entering he original entry.  Didn't know it was as bad as it appears now.

Note that inventory is "live".  The Valuation report does take into consideration future dated transactions.  So in your case the two would not tie until December 2015.