what is the maximum Limit for Tags for Unlimited License ?
Does Unlimited mean unlimited? Strictly speaking, no. I believe that PointID is an UInt32. This limits you to 4.2 billion tags, or 2 raised to the 32 power minus 1, or 4294967295.
So can your PI Data Archive host 4.2 billion tags? That depends upon the RAM and available disk space, but the realistic answer is probably not. Keep in mind an empty archive file for say 25 million tags would be quite huge in its own right. Empty!
What makes you think your import error is regarding the tag count? Have you checked the logs?
Could you specify the error that you got? How are you "importing" the tags ?
Refer 3157OSI8 - License File (pilicense.dat): What am I licensed for, How many data streams, What applications?
to obtain point count information for a license
Retrieving data ...