Assuming the message is "Out of memory or address space - texture quality may be too high" Then the source engine ran out of RAM or video memory (RAM but for video cards) , restart you computer first then change your page file size on your Hard drive, this can be done in control panel I think.
If this is your first time logging in after the migration (Feb 8, 2022), you must reset your password to log in. Follow this guide if you're having trouble