Besides the obvious (like incorrect password), this message occurs if you have a trailing space in the domain name. On the W95 client:
Cancel the Enter Network Password dialog box. This starts W95 without network connectivity.
Right-click the Network Neighborhood icon on the desktop, and then click Properties\Identification tab.
Retype the Computer name and in Workgroup, retype the domain name. Click OK, and then click Yes when you are prompted to restart your computer.