Sorry, this account is not active.

I had my client purchase membershi[ plug in for his site of which i am building, this has now happened twice in the build process, I build the site activate MEMBERSHIP, try to work out how to use it , leave the site for a couple of days, try to log back into the dashboard as the site and it wont let me in, SAYS Sorry, this account is not active.

this is so worrying as the first time it happened i had to wipe the site and start again ..

please help. this is driving me crazy.