Grails 2.4.4 file upload error when the file exists - grails

Question

I have an action that receives a file correctly and saves it to a destination folder without problems.
When the destination folder has a file with the same name, the method transferTo, first deletes the existing file, then copies the new one (http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/multipart/commons/CommonsMultipartFile.html#transferTo-java.io.File-).
But if the destination file exists, Grails is throwing this error, and the existing file is deleted but the uploaded one is not copied.
I'm working in WinXP, so I don't think it is a permissions issues (the file is deleted so I guess has nothing to do with permissions).
| Error 2015-05-24 23:47:58,199 [http-bio-8090-exec-3] ERROR errors.GrailsExceptionResolver - FileNotFoundException occurred when processing request: [POST] /ehr/test/upload - parameters:
doit: upload
overwrite: true
SYNCHRONIZER_TOKEN: 8deaf46b-b6ff-4362-ac70-7223f37ae806
SYNCHRONIZER_URI: /ehr/test/upload
opts\Signos.opt (Access is denied). Stacktrace follows:
Message: opts\Signos.opt (Access is denied)
Line | Method
->> 221 | <init> in java.io.FileOutputStream
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| 171 | <init> in ''
| 417 | write . . in org.apache.commons.fileupload.disk.DiskFileItem
| 85 | upload in test.TestController
| 198 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter
| 63 | doFilter in grails.plugin.cache.web.filter.AbstractFilter
| 1145 | runWorker in java.util.concurrent.ThreadPoolExecutor
| 615 | run in java.util.concurrent.ThreadPoolExecutor$Worker
^ 744 | run . . . in java.lang.Thread
The upload action looks like:
def upload(boolean overwrite)
{
if (params.doit)
{
def errors = []
def f = request.getFile('opt')
def xml = new String( f.getBytes() )
def destination = config.opt_repo + f.getOriginalFilename()
File fileDest = new File( destination )
if (!overwrite && fileDest.exists())
{
errors << "The OPT already exists, do you want to overwrite?"
return [errors: errors, ask_overwrite: true]
}
// Some validation logic here ...
if (errors.size() == 0)
{
// http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/multipart/commons/CommonsMultipartFile.html#transferTo-java.io.File-
// If the file exists, it will be deleted first
f.transferTo(fileDest)
}
}
}