VFP6/SP4 on Win2K-AS SP1

I created a database strictly through code. Somewhere along the line, after I had added about 40 tables, at random I get an error "Database is invalid. Please validate."

There is nothing else running in VFP and basically nothing else running on the computer. I just fire up the VFP IDE, run the .prg, and at random I get the error. My code is only made up of statements like these:

Create database....
Create table...
index on....
dbsetprop(column comments)
dbsetprop(table comments)

It's always halting when indexing, but it could be on any table in the code. It never halts anywhere else.