The SharePoint item being crawled returned an error when requesting data from the web service.

When using FAST search for SharePoint 2010 (F4SP) to crawl a content source that contains managed metadata in the field you might get this error

The SharePoint item being crawled returned an error when requesting data from the web service. ( Error from SharePoint site: *** Index was outside the bounds of the array. )

this is because one or more metadata field is filled with incorrect value. When you open it up it show something like this.

The red underline text means there's no term "Knowledge" in the Knowledge Themes metadata field.

if you leave this red text save in your item properties and run a crawling. You will get this error.

To solve this error

That's simple, correct the red underlined text in metadata field. then FAST search will crawl this item correctly.

Clear-FASTSearchContentCollection : Failed to communicate with the WCF service.

According to this title error when clear fast search index using PowerShell command.
Clear-FASTSearchContentCollection -Name sp
and I got this error
Failed to communicate with the WCF service.
then i changed user account to run this command by Shift + Right Click on FAST Search

Then log on as FAST service account to run this command instead of current account.

Hope this helps.

Download and Update patch on SharePoint Farm

Microsoft has been released SharePoint 2010 patch update for a while refer to the following links.

• Microsoft Office Updates 
• Updates for SharePoint Products 

then I downloaded the SP1 and August CU updates from the above site. Service Pack1 for many products

1. Documentum Search connector SP1
2. FAST Search for SharePoint SP1
3. FAST Search for SharePoint August CU
4. Office Web Apps SP1
5. SharePoint August CU
6. SharePoint SP1
7. SharePoint Designer SP1

All of their size around ~2GB. the SharePoint August CU size is about 1GB. I though there's a lot of bug in SharePoint.