I decide to create this specific title, because the error had been solved directly, and you don't need to read others tell the end...
So only I wanted to share with you my solution.

'm using a fresh sugar installation v. 5.5.2...

I wanted to import data from .csv to my potentials, and I got an error in step 3 to confirm the import data.
The error was multiple, in sugar it was error to import data, click here to see the report... and when I click, i got the error 403 from my server, access prohibited.

So, first i recheck back the chmod 755 for costum file, and 644 for the config.php

But, the error still the same.

Checking mysql database, the result was:

warning : Table is marked as crashed
error : Size of indexfile is: 9216 Should be: 11264
error : Size of datafile is: 8176 Should be: 8468
error : Corrupt
warning : Table is marked as crashed
error : Size of indexfile is: 1024 Should be: 27648
error : Corrupt

And after correct it, and all done, the error still the same...

SOLUTION:
The error message in dead appoint to the ../cache/import/error_1.csv.php where I guest that when we click in the report to open it, we get the 403 error message, because the file it's just created after the import operation, and I the credential was in chmod 660, so I couldn't open it to see what's their...

The direct reason, that one of the mandatory filed in the .csv file which i wanted to import, was empty, without value, meanwhile sure have it like mandatory, so the import are repoted.

When i repeat the import operation with any data in that field, all it's ok.

So, the problem aren't server problem in dead, neither Sugar problem, it's only the chmod because the file are newlly created within 660, and I couldn't execute it to see what's their...

Conclusion, the 403 message which you want to open, it's coming only to open the reason of wrong import, which you could find it in the ./costum/import/erro..php.

Enjoy it, enjoy Sugar...
Regards,