smart card status: the card is being shared by another process

Hi,

I plan to use Smart Card to unlock a drive that is being locked by BitLocker Drive Encryption. 

The certificate request content is:

[NewRequest]
Subject = "CN=BitLocker"
KeyLength = 2048
ProviderName = "SafeNet Smart Card Key Storage Provider"
KeySpec = "AT_KEYEXCHANGE" 
KeyUsage = "CERT_KEY_ENCIPHERMENT_KEY_USAGE"
KeyUsageProperty = "NCRYPT_ALLOW_DECRYPT_FLAG"
RequestType = Cert
SMIME = FALSE
[EnhancedKeyUsageExtension]
OID=1.3.6.1.4.1.311.67.1.1
The certificate is issued by my CA and is stored in the smart card. But when I choose "Use my smart card to unlock the drive" option 
and insert the smart card, this error appears in the smart card status part: "the card is being shared by another process"
The OS is windows 2008 R2. I have tried to do this on my windows 7 client, but the same occurs.
How can I fix it? Any help?